diff --git a/src/keyboard/ergodox.c b/src/keyboard/ergodox.c
index 12b5f32..a55bfb9 100644
--- a/src/keyboard/ergodox.c
+++ b/src/keyboard/ergodox.c
@@ -9,10 +9,9 @@
 
 #include "lib/data-types.h"
 
-#define KEYBOARD_INCLUDE_PRIVATE
 #include "ergodox/matrix.h"
-#include "ergodox/mcp23018.h"
-#include "ergodox/teensy-2-0.h"
+#include "ergodox/mcp23018--private.h"
+#include "ergodox/teensy-2-0--private.h"
 
 
 /* returns
diff --git a/src/keyboard/ergodox.h b/src/keyboard/ergodox.h
index 5174f31..00ba51e 100644
--- a/src/keyboard/ergodox.h
+++ b/src/keyboard/ergodox.h
@@ -16,7 +16,6 @@
 	#include "ergodox/layout.h"      // number of layers, layout
 	#include "ergodox/led.h"         // logical led controls
 	#include "ergodox/matrix.h"      // kb dimensions, matrix status
-	#include "ergodox/mcp23018.h"    // (nothing right now)
 	#include "ergodox/teensy-2-0.h"  // LED controls
 
 
diff --git a/src/keyboard/ergodox/layout.h b/src/keyboard/ergodox/layout.h
index 0cf5fee..e58eb51 100644
--- a/src/keyboard/ergodox/layout.h
+++ b/src/keyboard/ergodox/layout.h
@@ -15,8 +15,7 @@
 	#include "lib/data-types.h"
 	#include "lib/key-functions.h"  // for `kbfun_funptr_t`
 
-	#include "matrix.h"  // for number of rows and columns, and layout
-			     //   to matrix macros
+	#include "matrix.h"  // for number of rows and columns
 
 	// include the appropriate keyboard layout header
 	// for:
diff --git a/src/keyboard/ergodox/layout/qwerty.c b/src/keyboard/ergodox/layout/qwerty.c
index 51d04e1..ea8a8ac 100644
--- a/src/keyboard/ergodox/layout/qwerty.c
+++ b/src/keyboard/ergodox/layout/qwerty.c
@@ -14,8 +14,8 @@
 #include "lib/usb/usage-page/keyboard--short-names.h"
 #include "lib/key-functions.h"
 
-#define KEYBOARD_INCLUDE_PRIVATE
 #include "../matrix.h"
+#include "../matrix--private.h"
 #include "../layout.h"
 
 
@@ -26,12 +26,6 @@
 #define f_l_dec &kbfun_layer_dec
 
 
-// error check: everything below assumes these dimensions
-#if KB_LAYERS != 2 || KB_ROWS != 12 || KB_COLUMNS != 7
-	#error "Expecting different keyboard dimensions"
-#endif
-
-
 uint8_t PROGMEM _kb_layout[KB_LAYERS][KB_ROWS][KB_COLUMNS] = {
 // ----------------------------------------------------------------------------
 	LAYER(  // layer 0: default
@@ -41,7 +35,7 @@ uint8_t PROGMEM _kb_layout[KB_LAYERS][KB_ROWS][KB_COLUMNS] = {
 _grave,    _1,      _2,      _3,      _4,      _5,  _equal,
 _tab,      _Q,      _W,      _E,      _R,      _T,  _esc,
 _capsLock, _A,      _S,      _D,      _F,      _G,
-_shiftL,   _Z,      _X,      _C,      _V,      _B,  0/*inc*/,
+_shiftL,   _Z,      _X,      _C,      _V,      _B,   0,
 _guiL,     _arrowL, _arrowU, _arrowD, _arrowR,
                                                  _bs,
                                                  _del,     _ctrlL,
@@ -50,7 +44,7 @@ _guiL,     _arrowL, _arrowU, _arrowD, _arrowR,
          _backslash, _6, _7,      _8,      _9,      _0,         _dash,
          _bracketL,  _Y, _U,      _I,      _O,      _P,         _bracketR,
                      _H, _J,      _K,      _L,      _semicolon, _quote,
-          0/*inc*/,  _N, _M,      _comma,  _period, _slash,     _shiftR,
+          0,         _N, _M,      _comma,  _period, _slash,     _shiftR,
                          _arrowL, _arrowD, _arrowU, _arrowR,    _guiR,
             _space,
 _ctrlR,     _enter,
@@ -63,17 +57,17 @@ _altR,  _pageU, _pageD ),
 0, _F1,        _F2,        _F3,       _F4,       _F5,       _F11,
 0, _braceL_kp, _braceR_kp, _bracketL, _bracketR,  0,        _esc,
 0, _semicolon, _slash,     _dash,      0,        _colon_kp,
-0,  0,          0,          0,         0,         0,        0/*dec*/,
+0,  0,          0,          0,         0,         0,         0,
 0, _arrowL,    _arrowU,    _arrowD,   _arrowR,
                                                        _bs,
                                                        _del,     _ctrlL,
                                                     _end, _home, _altL,
 // right hand
-       _F12,     _F6,       _F7,     _F8,        _F9,        _F10,          0,
-        0,        0,        _dash,   _lt_kp,     _gt_kp,     _currencyUnit, 0,
-                 _backslash, 0,      _parenL_kp, _parenR_kp, _equal,        0,
-       0/*dec*/, _mul_kp,    0,       0,          0,          0,            0,
-                            _arrowL, _arrowD,    _arrowU,    _arrowR,       0,
+         _F12, _F6,       _F7,     _F8,        _F9,        _F10,          0,
+          0,    0,        _dash,   _lt_kp,     _gt_kp,     _currencyUnit, 0,
+               _backslash, 0,      _parenL_kp, _parenR_kp, _equal,        0,
+          0,   _mul_kp,    0,       0,          0,          0,            0,
+                          _arrowL, _arrowD,    _arrowU,    _arrowR,       0,
             _space,
 _ctrlR,     _enter,
 _altR,  _pageU, _pageD )
@@ -139,28 +133,6 @@ NULL,
 f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
 f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
 f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
-f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,   NULL,
-f_relea,f_relea,f_relea,f_relea,f_relea,
-                                           f_relea,
-                                           f_relea,  f_relea,
-                                       f_relea,f_relea,f_relea,
-// right hand
-       f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
-       f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
-               f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
-          NULL,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
-                       f_relea,f_relea,f_relea,f_relea,f_relea,
-          f_relea,
-f_relea,  f_relea,
-f_relea,f_relea,f_relea ),
-// ----------------------------------------------------------------------------
-	LAYER(  // layer 1: function and symbol keys
-// unused
-NULL,
-// left hand
-f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
-f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
-f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
 f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,f_l_dec,
 f_relea,f_relea,f_relea,f_relea,f_relea,
                                            f_relea,
@@ -174,6 +146,28 @@ f_relea,f_relea,f_relea,f_relea,f_relea,
                        f_relea,f_relea,f_relea,f_relea,f_relea,
           f_relea,
 f_relea,  f_relea,
+f_relea,f_relea,f_relea ),
+// ----------------------------------------------------------------------------
+	LAYER(  // layer 1: function and symbol keys
+// unused
+NULL,
+// left hand
+f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
+f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
+f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
+f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,   NULL,
+f_relea,f_relea,f_relea,f_relea,f_relea,
+                                           f_relea,
+                                           f_relea,  f_relea,
+                                       f_relea,f_relea,f_relea,
+// right hand
+       f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
+       f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
+               f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
+          NULL,f_relea,f_relea,f_relea,f_relea,f_relea,f_relea,
+                       f_relea,f_relea,f_relea,f_relea,f_relea,
+          f_relea,
+f_relea,  f_relea,
 f_relea,f_relea,f_relea )
 // ----------------------------------------------------------------------------
 };
diff --git a/src/keyboard/ergodox/matrix--private.h b/src/keyboard/ergodox/matrix--private.h
new file mode 100644
index 0000000..3094eca
--- /dev/null
+++ b/src/keyboard/ergodox/matrix--private.h
@@ -0,0 +1,96 @@
+/* ----------------------------------------------------------------------------
+ * ergoDOX: keyboard matrix specific exports : private
+ * ----------------------------------------------------------------------------
+ * Copyright (c) 2012 Ben Blazak <benblazak.dev@gmail.com>
+ * Released under The MIT License (MIT) (see "license.md")
+ * Project located at <https://github.com/benblazak/ergodox-firmware>
+ * ------------------------------------------------------------------------- */
+
+
+#ifndef MATRIX_h_PRIVATE
+	#define MATRIX_h_PRIVATE
+
+	/* mapping from spatial position to matrix position
+	 * - spatial position: where the key is spatially, relative to other
+	 *   keys both on the keyboard and in the layout
+	 * - matrix position: the coordinate in the matrix to which a key is
+	 *   scanned by the update functions
+	 *
+	 * - location numbers are in the format `row##column`, where both 'row'
+	 *   and 'column' are single digit hex numbers corresponding to the
+	 *   matrix position (which also corresponds to the row and column pin
+	 *   labels used in the teensy and mcp23018 files)
+	 * - coordinates not listed are unused
+	 *
+	 * --- other info -----------------------------------------------------
+	 *           rows x columns = positions;  assigned,  unassigned
+	 * per hand:    6 x 7       = 42;         38,        4
+	 *    total:   12 x 7       = 84;         76,        8
+	 *
+	 * left hand  : cols 0..6, rows 6..B
+	 * right hand : cols 0..6, rows 0..5
+	 * --------------------------------------------------------------------
+	 */
+	#define LAYER(						\
+			/* for unused positions */		\
+			na,					\
+								\
+			/* left hand, spatial positions */	\
+			kB6,kB5,kB4,kB3,kB2,kB1,kB0,		\
+			kA6,kA5,kA4,kA3,kA2,kA1,kA0,		\
+			k96,k95,k94,k93,k92,k91,		\
+			k86,k85,k84,k83,k82,k81,k80,		\
+			k76,k75,k74,k73,k72,			\
+			                      k64,		\
+			                      k63,  k60,	\
+			                    k65,k62,k61,	\
+								\
+			/* right hand, spatial positions */	\
+			    k50,k51,k52,k53,k54,k55,k56,	\
+			    k40,k41,k42,k43,k44,k45,k46,	\
+			        k31,k32,k33,k34,k35,k36,	\
+			    k20,k21,k22,k23,k24,k25,k26,	\
+			            k12,k13,k14,k15,k16,	\
+			      k04,				\
+			k00,  k03,				\
+			k01,k02,k05 )				\
+								\
+		/* matrix positions */				\
+		{ { k00,k01,k02,k03,k04,k05, na,},		\
+		  {  na, na,k12,k13,k14,k15,k16,},		\
+		  { k20,k21,k22,k23,k24,k25,k26,},		\
+		  {  na,k31,k32,k33,k34,k35,k36,},		\
+		  { k40,k41,k42,k43,k44,k45,k46,},		\
+		  { k50,k51,k52,k53,k54,k55,k56,},		\
+		  { k60,k61,k62,k63,k64,k65, na,},		\
+		  {  na, na,k72,k73,k74,k75,k76,},		\
+		  { k80,k81,k82,k83,k84,k85,k86,},		\
+		  {  na,k91,k92,k93,k94,k95,k96,},		\
+		  { kA0,kA1,kA2,kA3,kA4,kA5,kA6,},		\
+		  { kB0,kB1,kB2,kB3,kB4,kB5,kB6 } }
+
+
+	#define LAYER_SET_ALL(na, kxx)				\
+		LAYER(						\
+			na,					\
+								\
+			kxx,kxx,kxx,kxx,kxx,kxx,kxx,		\
+			kxx,kxx,kxx,kxx,kxx,kxx,kxx,		\
+			kxx,kxx,kxx,kxx,kxx,kxx,		\
+			kxx,kxx,kxx,kxx,kxx,kxx,kxx,		\
+			kxx,kxx,kxx,kxx,kxx,			\
+			                      kxx,		\
+			                      kxx,  kxx,	\
+			                    kxx,kxx,kxx,	\
+								\
+			    kxx,kxx,kxx,kxx,kxx,kxx,kxx,	\
+			    kxx,kxx,kxx,kxx,kxx,kxx,kxx,	\
+			        kxx,kxx,kxx,kxx,kxx,kxx,	\
+			    kxx,kxx,kxx,kxx,kxx,kxx,kxx,	\
+			            kxx,kxx,kxx,kxx,kxx,	\
+			      kxx,				\
+			kxx,  kxx,				\
+			kxx,kxx,kxx )
+
+#endif
+
diff --git a/src/keyboard/ergodox/matrix.c b/src/keyboard/ergodox/matrix.c
index 3a1f9e7..d5e6b93 100644
--- a/src/keyboard/ergodox/matrix.c
+++ b/src/keyboard/ergodox/matrix.c
@@ -10,6 +10,7 @@
 #include "lib/data-types.h"
 
 #include "matrix.h"
+#include "matrix--private.h"
 
 
 static bool _kb_is_pressed[KB_ROWS][KB_COLUMNS];
diff --git a/src/keyboard/ergodox/matrix.h b/src/keyboard/ergodox/matrix.h
index ce499b5..600f311 100644
--- a/src/keyboard/ergodox/matrix.h
+++ b/src/keyboard/ergodox/matrix.h
@@ -18,93 +18,5 @@
 	extern bool (*kb_is_pressed)[KB_ROWS][KB_COLUMNS];
 	extern bool (*kb_was_pressed)[KB_ROWS][KB_COLUMNS];
 
-
-	#ifdef KEYBOARD_INCLUDE_PRIVATE
-
-		/* mapping from spatial position to matrix position
-		 * - spatial position: where the key is spatially, relative to
-		 *   other keys both on the keyboard and in the layout
-		 * - matrix position: the coordinate in the matrix to which
-		 *   a key is scanned by the update functions
-		 *
-		 * - location numbers are in the format `row##column`, where
-		 *   both 'row' and 'column' are single digit hex numbers
-		 *   corresponding to the matrix position (which also
-		 *   corresponds to the row and column pin labels used in the
-		 *   teensy and mcp23018 files)
-		 * - coordinates not listed are unused
-		 *
-		 * --- other info ---------------------------------------------
-		 *           rows x columns = positions;  assigned,  unassigned
-		 * per hand:    6 x 7       = 42;         38,        4
-		 *    total:   12 x 7       = 84;         76,        8
-		 *
-		 * left hand  : cols 0..6, rows 6..B
-		 * right hand : cols 0..6, rows 0..5
-		 * ------------------------------------------------------------
-		 */
-		#define LAYER(						\
-				/* for unused positions */		\
-				na,					\
-									\
-				/* left hand, spatial positions */	\
-				kB6,kB5,kB4,kB3,kB2,kB1,kB0,		\
-				kA6,kA5,kA4,kA3,kA2,kA1,kA0,		\
-				k96,k95,k94,k93,k92,k91,		\
-				k86,k85,k84,k83,k82,k81,k80,		\
-				k76,k75,k74,k73,k72,			\
-				                      k64,		\
-				                      k63,  k60,	\
-				                    k65,k62,k61,	\
-									\
-				/* right hand, spatial positions */	\
-				    k50,k51,k52,k53,k54,k55,k56,	\
-				    k40,k41,k42,k43,k44,k45,k46,	\
-				        k31,k32,k33,k34,k35,k36,	\
-				    k20,k21,k22,k23,k24,k25,k26,	\
-				            k12,k13,k14,k15,k16,	\
-				      k04,				\
-				k00,  k03,				\
-				k01,k02,k05 )				\
-									\
-			/* matrix positions */				\
-			{ { k00,k01,k02,k03,k04,k05, na,},		\
-			  {  na, na,k12,k13,k14,k15,k16,},		\
-			  { k20,k21,k22,k23,k24,k25,k26,},		\
-			  {  na,k31,k32,k33,k34,k35,k36,},		\
-			  { k40,k41,k42,k43,k44,k45,k46,},		\
-			  { k50,k51,k52,k53,k54,k55,k56,},		\
-			  { k60,k61,k62,k63,k64,k65, na,},		\
-			  {  na, na,k72,k73,k74,k75,k76,},		\
-			  { k80,k81,k82,k83,k84,k85,k86,},		\
-			  {  na,k91,k92,k93,k94,k95,k96,},		\
-			  { kA0,kA1,kA2,kA3,kA4,kA5,kA6,},		\
-			  { kB0,kB1,kB2,kB3,kB4,kB5,kB6 } }
-
-
-		#define LAYER_SET_ALL(na, kxx)				\
-			LAYER(						\
-				na,					\
-									\
-				kxx,kxx,kxx,kxx,kxx,kxx,kxx,		\
-				kxx,kxx,kxx,kxx,kxx,kxx,kxx,		\
-				kxx,kxx,kxx,kxx,kxx,kxx,		\
-				kxx,kxx,kxx,kxx,kxx,kxx,kxx,		\
-				kxx,kxx,kxx,kxx,kxx,			\
-				                      kxx,		\
-				                      kxx,  kxx,	\
-				                    kxx,kxx,kxx,	\
-									\
-				    kxx,kxx,kxx,kxx,kxx,kxx,kxx,	\
-				    kxx,kxx,kxx,kxx,kxx,kxx,kxx,	\
-				        kxx,kxx,kxx,kxx,kxx,kxx,	\
-				    kxx,kxx,kxx,kxx,kxx,kxx,kxx,	\
-				            kxx,kxx,kxx,kxx,kxx,	\
-				      kxx,				\
-				kxx,  kxx,				\
-				kxx,kxx,kxx )
-
-	#endif
-
 #endif
 
diff --git a/src/keyboard/ergodox/mcp23018.h b/src/keyboard/ergodox/mcp23018--private.h
similarity index 62%
rename from src/keyboard/ergodox/mcp23018.h
rename to src/keyboard/ergodox/mcp23018--private.h
index ef29523..a48b9b4 100644
--- a/src/keyboard/ergodox/mcp23018.h
+++ b/src/keyboard/ergodox/mcp23018--private.h
@@ -1,5 +1,5 @@
 /* ----------------------------------------------------------------------------
- * ergoDOX controller: MCP23018 specific exports
+ * ergoDOX controller: MCP23018 specific exports : private
  * ----------------------------------------------------------------------------
  * Copyright (c) 2012 Ben Blazak <benblazak.dev@gmail.com>
  * Released under The MIT License (MIT) (see "license.md")
@@ -7,20 +7,16 @@
  * ------------------------------------------------------------------------- */
 
 
-#ifndef MCP23018_h
-	#define MCP23018_h
+#ifndef MCP23018_h_PRIVATE
+	#define MCP23018_h_PRIVATE
 
 	#include "lib/data-types.h"
+	#include "matrix.h"
 
-	#ifdef KEYBOARD_INCLUDE_PRIVATE
+	#define MCP23018_TWI_ADDRESS 0b0100000
 
-		#define MCP23018_TWI_ADDRESS 0b0100000
-
-		uint8_t mcp23018_init(void);
-		uint8_t mcp23018_update_matrix(
-				bool matrix[KB_ROWS][KB_COLUMNS] );
-
-	#endif
+	uint8_t mcp23018_init(void);
+	uint8_t mcp23018_update_matrix( bool matrix[KB_ROWS][KB_COLUMNS] );
 
 #endif
 
diff --git a/src/keyboard/ergodox/mcp23018.c b/src/keyboard/ergodox/mcp23018.c
index ca960a1..793d332 100644
--- a/src/keyboard/ergodox/mcp23018.c
+++ b/src/keyboard/ergodox/mcp23018.c
@@ -11,9 +11,8 @@
 #include "lib/data-types.h"
 #include "lib/twi.h"  // `TWI_FREQ` defined in "teensy-2-0.c"
 
-#define KEYBOARD_INCLUDE_PRIVATE
 #include "matrix.h"
-#include "mcp23018.h"
+#include "mcp23018--private.h"
 
 
 // register addresses (see "mcp23018.md")
diff --git a/src/keyboard/ergodox/teensy-2-0--private.h b/src/keyboard/ergodox/teensy-2-0--private.h
new file mode 100644
index 0000000..231e608
--- /dev/null
+++ b/src/keyboard/ergodox/teensy-2-0--private.h
@@ -0,0 +1,19 @@
+/* ----------------------------------------------------------------------------
+ * ergoDOX controller: Teensy 2.0 specific exports : private
+ * ----------------------------------------------------------------------------
+ * Copyright (c) 2012 Ben Blazak <benblazak.dev@gmail.com>
+ * Released under The MIT License (MIT) (see "license.md")
+ * Project located at <https://github.com/benblazak/ergodox-firmware>
+ * ------------------------------------------------------------------------- */
+
+
+#ifndef TEENSY_2_0_h_PRIVATE
+	#define TEENSY_2_0_h_PRIVATE
+
+	#include "matrix.h"
+
+	uint8_t teensy_init(void);
+	uint8_t teensy_update_matrix( bool matrix[KB_ROWS][KB_COLUMNS] );
+
+#endif
+
diff --git a/src/keyboard/ergodox/teensy-2-0.c b/src/keyboard/ergodox/teensy-2-0.c
index f09d033..74b68cf 100644
--- a/src/keyboard/ergodox/teensy-2-0.c
+++ b/src/keyboard/ergodox/teensy-2-0.c
@@ -13,9 +13,9 @@
 #define TWI_FREQ 400000
 #include "lib/twi.h"
 
-#define KEYBOARD_INCLUDE_PRIVATE
 #include "matrix.h"
 #include "teensy-2-0.h"
+#include "teensy-2-0--private.h"
 
 
 // processor frequency (from <http://www.pjrc.com/teensy/prescaler.html>)
diff --git a/src/keyboard/ergodox/teensy-2-0.h b/src/keyboard/ergodox/teensy-2-0.h
index 048072d..c43714f 100644
--- a/src/keyboard/ergodox/teensy-2-0.h
+++ b/src/keyboard/ergodox/teensy-2-0.h
@@ -13,8 +13,6 @@
 	#include <avr/io.h>  // for the register macros
 	#include "lib/data-types.h"
 
-	#include "matrix.h"
-
 
 	// LED control
 	#define _led_1_on()           (DDRB |=  (1<<6))
@@ -53,14 +51,5 @@
 		_led_3_set_percent(n);		\
 		} while(0)
 
-
-	#ifdef KEYBOARD_INCLUDE_PRIVATE
-
-		uint8_t teensy_init(void);
-		uint8_t teensy_update_matrix(
-				bool matrix[KB_ROWS][KB_COLUMNS] );
-
-	#endif
-
 #endif
 
diff --git a/src/lib/key-functions.c b/src/lib/key-functions.c
index 9d55bd5..53c6011 100644
--- a/src/lib/key-functions.c
+++ b/src/lib/key-functions.c
@@ -19,16 +19,13 @@
 #include "key-functions.h"
 
 
-void kbfun_press(
-		uint8_t keycode, uint8_t * current_layer,
-		uint8_t * row,   uint8_t * col ) {
-
+void kbfun_press( KBFUN_FUNCTION_ARGS ) {
 	// no-op
-	if (keycode == 0)
+	if (keycode_ == 0)
 		return;
 
 	// modifier keys
-	switch (keycode) {
+	switch (keycode_) {
 		case KEY_LeftControl:  keyboard_modifier_keys |= (1<<0);
 				       return;
 		case KEY_LeftShift:    keyboard_modifier_keys |= (1<<1);
@@ -50,21 +47,18 @@ void kbfun_press(
 	// all others
 	for (uint8_t i=0; i<6; i++)
 		if (keyboard_keys[i] == 0) {
-			keyboard_keys[i] = keycode;
-			break;
+			keyboard_keys[i] = keycode_;
+			return;
 		}
 }
 
-void kbfun_release(
-		uint8_t keycode, uint8_t * current_layer,
-		uint8_t * row,   uint8_t * col ) {
-
+void kbfun_release( KBFUN_FUNCTION_ARGS ) {
 	// no-op
-	if (keycode == 0)
+	if (keycode_ == 0)
 		return;
 
 	// modifier keys
-	switch (keycode) {
+	switch (keycode_) {
 		case KEY_LeftControl:  keyboard_modifier_keys &= ~(1<<0);
 				       return;
 		case KEY_LeftShift:    keyboard_modifier_keys &= ~(1<<1);
@@ -85,37 +79,30 @@ void kbfun_release(
 
 	// all others
 	for (uint8_t i=0; i<6; i++)
-		if (keyboard_keys[i] == keycode) {
+		if (keyboard_keys[i] == keycode_) {
 			keyboard_keys[i] = 0;
-			break;
+			return;
 		}
 }
 
 // TODO:
-// - allocate 10 layers, by default (overrideable in the map specific .h)
-// - implement having different keys using different layers
 // - implement two shifts => capslock
 // - implement layer lock key combos (make a function to switch to a specific
 //   layer)
 
-void kbfun_layer_inc(
-		uint8_t keycode, uint8_t * current_layer,
-		uint8_t * row,   uint8_t * col ) {
-
-	if (*current_layer < (KB_LAYERS-1))
-		(*current_layer)++;
-	// else do nothing
+void kbfun_layer_inc( KBFUN_FUNCTION_ARGS ) {
+	for (uint8_t row=0; row<KB_ROWS; row++)
+		for (uint8_t col=0; col<KB_COLUMNS; col++)
+			if ((*current_layers_)[row][col] < (KB_LAYERS-1))
+				((*current_layers_)[row][col])++;
+			// else do nothing
 }
 
-void kbfun_layer_dec(
-		uint8_t keycode, uint8_t * current_layer,
-		uint8_t * row,   uint8_t * col ) {
-
-	if (*current_layer > 0)
-		(*current_layer)--;
-	// else do nothing
+void kbfun_layer_dec( KBFUN_FUNCTION_ARGS ) {
+	for (uint8_t row=0; row<KB_ROWS; row++)
+		for (uint8_t col=0; col<KB_COLUMNS; col++)
+			if ((*current_layers_)[row][col] > 0)
+				((*current_layers_)[row][col])--;
+			// else do nothing
 }
 
-
-// ----------------------------------------------------------------------------
-
diff --git a/src/lib/key-functions.h b/src/lib/key-functions.h
index fa4a819..b709474 100644
--- a/src/lib/key-functions.h
+++ b/src/lib/key-functions.h
@@ -12,22 +12,40 @@
 
 	#include "lib/data-types.h"
 
-	typedef void (*kbfun_funptr_t)(
-			uint8_t,   uint8_t *,
-			uint8_t *, uint8_t * );
+	// --------------------------------------------------------------------
+	// include the appropriate 'matrix.h'
+	// -------
+	// we're not simply including 'keyboard.h' here because this header is
+	// meant to be included by 'keyboard/layout/*.c', which is indirectly
+	// included by 'keyboard.h'; and that would lead to a circular include,
+	// which gcc might (depending on the order of include statements it
+	// encounters) deal with by processing this file before 'matrix.h',
+	// which would give us undefined macros here
+	#undef _str
+	#undef _expstr
+	#undef _inc
+	#define _str(s) #s          // stringify
+	#define _expstr(s) _str(s)  // expand -> stringify
+	#define _inc _expstr(keyboard/MAKEFILE_KEYBOARD/matrix.h)  // inc(lude)
+	#include _inc
+	#undef _str
+	#undef _expstr
+	#undef _inc
+	// --------------------------------------------------------------------
 
-	void kbfun_press(
-			uint8_t keycode, uint8_t * current_layer,
-			uint8_t * row,   uint8_t * col );
-	void kbfun_release(
-			uint8_t keycode, uint8_t * current_layer,
-			uint8_t * row,   uint8_t * col );
-	void kbfun_layer_inc(
-			uint8_t keycode, uint8_t * current_layer,
-			uint8_t * row,   uint8_t * col );
-	void kbfun_layer_dec(
-			uint8_t keycode, uint8_t * current_layer,
-			uint8_t * row,   uint8_t * col );
+
+	#define KBFUN_FUNCTION_ARGS					\
+		uint8_t keycode_,					\
+		uint8_t (*current_layers_)[KB_ROWS][KB_COLUMNS],	\
+		uint8_t (*pressed_layers_)[KB_ROWS][KB_COLUMNS],	\
+		uint8_t * row_, uint8_t * col_
+
+	typedef void (*kbfun_funptr_t)( KBFUN_FUNCTION_ARGS );
+
+	void kbfun_press     ( KBFUN_FUNCTION_ARGS );
+	void kbfun_release   ( KBFUN_FUNCTION_ARGS );
+	void kbfun_layer_inc ( KBFUN_FUNCTION_ARGS );
+	void kbfun_layer_dec ( KBFUN_FUNCTION_ARGS );
 
 #endif
 
diff --git a/src/main.c b/src/main.c
index eaa76d4..340873a 100644
--- a/src/main.c
+++ b/src/main.c
@@ -27,7 +27,10 @@ int main(void) {
 	kb_led_state_ready();
 
 	for (;;) {
-		static uint8_t current_layer = 0;
+		// the current layer for each key
+		static uint8_t current_layers[KB_ROWS][KB_COLUMNS];
+		// the layer each key was on when it was last pressed
+		static uint8_t pressed_layers[KB_ROWS][KB_COLUMNS];
 
 		// swap `kb_is_pressed` and `kb_was_pressed`, then update
 		bool (*temp)[KB_ROWS][KB_COLUMNS] = kb_was_pressed;
@@ -36,32 +39,44 @@ int main(void) {
 
 		kb_update_matrix(*kb_is_pressed);
 
-		// call the appropriate function for each key, then send the usb report
-		// if necessary
+		// call the appropriate function for each key(press|release), then send
+		// the usb report if necessary
+		// -------
 		// - everything else is the key function's responsibility; see the
 		//   keyboard layout file ("keyboard/ergodox/layout/*.c") for which key
 		//   is assigned which function (per layer), and "lib/key-functions.c"
 		//   for their definitions
+		// - anything passed to the key function by reference may be changed
+		//   after the call
 		for (uint8_t row=0; row<KB_ROWS; row++) {
 			for (uint8_t col=0; col<KB_COLUMNS; col++) {
+
 				bool is_pressed = (*kb_is_pressed)[row][col];
 				bool was_pressed = (*kb_was_pressed)[row][col];
+
 				if (is_pressed != was_pressed) {
+
 					if (is_pressed) {
+						uint8_t current_layer = current_layers[row][col];
+						pressed_layers[row][col] = current_layer;
 						kbfun_funptr_t press_function =
-								kb_layout_press_get(current_layer, row, col);
+							kb_layout_press_get(current_layer, row, col);
 						if (press_function) {
 							(*press_function)(
 									kb_layout_get(current_layer, row, col),
-									&current_layer, &row, &col );
+									&current_layers, &pressed_layers,
+									&row, &col );
 						}
+
 					} else {
+						uint8_t pressed_layer = pressed_layers[row][col];
 						kbfun_funptr_t release_function =
-								kb_layout_release_get(current_layer, row, col);
+							kb_layout_release_get(pressed_layer, row, col);
 						if (release_function) {
 							(*release_function)(
-									kb_layout_get(current_layer, row, col),
-									&current_layer, &row, &col );
+									kb_layout_get(pressed_layer, row, col),
+									&current_layers, &pressed_layers,
+									&row, &col );
 						}
 					}