diff --git a/examples/AppSwitcher/AppSwitcher.ino b/examples/AppSwitcher/AppSwitcher.ino
index e8b231d5..7303cc33 100644
--- a/examples/AppSwitcher/AppSwitcher.ino
+++ b/examples/AppSwitcher/AppSwitcher.ino
@@ -24,7 +24,7 @@
 #include "Macros.h"
 
 /* *INDENT-OFF* */
-const Key keymaps[][ROWS][COLS] PROGMEM = {
+KEYMAPS(
   [0] = KEYMAP_STACKED
   (
    Key_NoKey,    Key_1, Key_2, Key_3, Key_4, Key_5, Key_NoKey,
@@ -43,7 +43,7 @@ const Key keymaps[][ROWS][COLS] PROGMEM = {
    Key_RightShift, Key_RightAlt, Key_Spacebar, Key_RightControl,
    M(M_APPCANCEL)
    ),
-};
+)
 /* *INDENT-ON* */
 
 
diff --git a/examples/Kaleidoscope/Kaleidoscope.ino b/examples/Kaleidoscope/Kaleidoscope.ino
index 64c42bb7..e3a90086 100644
--- a/examples/Kaleidoscope/Kaleidoscope.ino
+++ b/examples/Kaleidoscope/Kaleidoscope.ino
@@ -57,14 +57,13 @@
                                               Key_KeymapNext_Momentary,         Key_KeymapNext_Momentary \
 )
 
-const Key keymaps[][ROWS][COLS] PROGMEM = {
+KEYMAPS(
   QWERTY,
   GENERIC_FN2,
   NUMPAD
+)
 
 
-};
-
 static kaleidoscope::LEDSolidColor solidRed(60, 0, 0);
 static kaleidoscope::LEDSolidColor solidOrange(60, 20, 0);
 static kaleidoscope::LEDSolidColor solidYellow(40, 35, 0);
diff --git a/src/layers.cpp b/src/layers.cpp
index 702672a8..b647510a 100644
--- a/src/layers.cpp
+++ b/src/layers.cpp
@@ -8,6 +8,11 @@ Key Layer_::liveCompositeKeymap[ROWS][COLS];
 uint8_t Layer_::activeLayers[ROWS][COLS];
 Key(*Layer_::getKey)(uint8_t layer, byte row, byte col) = Layer.getKeyFromPROGMEM;
 
+// The total number of defined layers in the firmware sketch keymaps[]
+// array. If the keymap wasn't defined using CREATE_KEYMAP() in the
+// sketch file, layer_count gets the default value of zero.
+uint8_t layer_count __attribute__((weak)) = 0;
+
 static void handleKeymapKeyswitchEvent(Key keymapEntry, uint8_t keyState) {
   if (keymapEntry.keyCode >= LAYER_SHIFT_OFFSET) {
     uint8_t target = keymapEntry.keyCode - LAYER_SHIFT_OFFSET;
@@ -125,6 +130,11 @@ void Layer_::move(uint8_t layer) {
 }
 
 void Layer_::on(uint8_t layer) {
+  // If we're trying to turn on a layer that doesn't exist, abort (but
+  // if the keymap wasn't defined using CREATE_KEYMAP(), proceed anyway
+  if (layer_count != 0 && layer >= layer_count)
+    return;
+
   bool wasOn = isOn(layer);
 
   bitSet(LayerState, layer);
diff --git a/src/layers.h b/src/layers.h
index c9b2cd8b..3d4ae465 100644
--- a/src/layers.h
+++ b/src/layers.h
@@ -4,6 +4,14 @@
 #include "key_defs.h"
 #include KALEIDOSCOPE_HARDWARE_H
 
+// Macro for defining the keymap. This should be used in the sketch
+// file (*.ino) to define the keymap[] array that holds the user's
+// layers. It also computes the number of layers in that keymap.
+#define KEYMAPS(layers...)				\
+  const Key keymaps[][ROWS][COLS] PROGMEM = { layers };		\
+  uint8_t layer_count = sizeof(keymaps) / sizeof(*keymaps);
+
+
 class Layer_ {
  public:
   Layer_(void);