diff --git a/src/keyboard/controller.c b/src/keyboard/controller.c
index 8462676..5cfb3af 100644
--- a/src/keyboard/controller.c
+++ b/src/keyboard/controller.c
@@ -1320,12 +1320,10 @@ void usb_debug_printf(const char *fmt, ...) {
   }
   usb_debug_flush_output();
 }
-#endif
 
-#ifdef KBD_DEBUG
-#define debug_print(s)          	usb_debug_print(PSTR(s))
-#define debug_printf(s, args...)	usb_debug_printf(PSTR(s), args)
-#else
-#define debug_print(s)
-#define debug_printf(...)
+void usb_debug_free_memory() {
+  extern int __heap_start, *__brkval; int v, free;
+  free = (int) &v - (__brkval == 0 ? (int) &__heap_start : (int) __brkval);
+  debug_printf("free memory: %d bytes\n", free);
+}
 #endif
diff --git a/src/keyboard/controller.h b/src/keyboard/controller.h
index c04da2c..d2a9cb3 100644
--- a/src/keyboard/controller.h
+++ b/src/keyboard/controller.h
@@ -207,8 +207,16 @@ extern uint16_t consumer_key;
 
 extern volatile uint8_t debug_flush_timer;
 
+void usb_debug_free_memory(void);
 void usb_debug_print(const char *s);
 void usb_debug_printf(const char *fmt, ...);
+int8_t usb_debug_putchar(char c);
+void usb_debug_flush_output(void);
 
-int8_t usb_debug_putchar(char c);	// transmit a character
-void usb_debug_flush_output(void);  	// immediately transmit any buffered output
+#ifdef KBD_DEBUG
+#define debug_print(s)          	usb_debug_print(PSTR(s))
+#define debug_printf(s, args...)	usb_debug_printf(PSTR(s), args)
+#else
+#define debug_print(s)
+#define debug_printf(...)
+#endif