diff --git a/src/Arduboy2Core.cpp b/src/Arduboy2Core.cpp
index 7ccbaae..cef7f21 100644
--- a/src/Arduboy2Core.cpp
+++ b/src/Arduboy2Core.cpp
@@ -73,6 +73,10 @@ const PROGMEM uint8_t lcdBootProgram[] = {
 };
 
 
+//========================================
+//========== class Arduboy2Core ==========
+//========================================
+
 Arduboy2Core::Arduboy2Core() { }
 
 void Arduboy2Core::boot()
@@ -572,11 +576,12 @@ void Arduboy2Core::exitToBootloader()
   while (true) { }
 }
 
-// Replacement main() that eliminates the USB stack code.
-// Used by the ARDUBOY_NO_USB macro. This should not be called
-// directly from a sketch.
 
-void Arduboy2Core::mainNoUSB()
+//=========================================
+//========== class Arduboy2NoUSB ==========
+//=========================================
+
+void Arduboy2NoUSB::mainNoUSB()
 {
   // disable USB
   UDCON = _BV(DETACH);
@@ -598,11 +603,11 @@ void Arduboy2Core::mainNoUSB()
   bitClear(DOWN_BUTTON_DDR, DOWN_BUTTON_BIT);
 
   // Delay to give time for the pin to be pulled high if it was floating
-  delayShort(10);
+  Arduboy2Core::delayShort(10);
 
   // if the DOWN button is pressed
   if (bitRead(DOWN_BUTTON_PORTIN, DOWN_BUTTON_BIT) == 0) {
-    exitToBootloader();
+    Arduboy2Core::exitToBootloader();
   }
 
   // The remainder is a copy of the Arduino main() function with the
diff --git a/src/Arduboy2Core.h b/src/Arduboy2Core.h
index 13cc73d..d1d4763 100644
--- a/src/Arduboy2Core.h
+++ b/src/Arduboy2Core.h
@@ -248,9 +248,9 @@
 /** \brief
  * Eliminate the USB stack to free up code space.
  *
- * \note
- * **WARNING:** Removing the USB code will make it impossible for sketch
- * uploader programs to automatically force a reset into the bootloader!
+ * \warning
+ * Removing the USB code will make it impossible for sketch uploader
+ * programs to automatically force a reset into the bootloader!
  * This means that a user will manually have to invoke a reset in order to
  * upload a new sketch, after one without USB has be been installed.
  * Be aware that the timing for the point that a reset must be initiated can
@@ -303,10 +303,20 @@
  */
 #define ARDUBOY_NO_USB int main() __attribute__ ((OS_main)); \
 int main() { \
-  Arduboy2Core::mainNoUSB(); \
+  Arduboy2NoUSB::mainNoUSB(); \
   return 0; \
 }
 
+// A replacement for the Arduino main() function that eliminates the USB code.
+// Used by the ARDUBOY_NO_USB macro.
+class Arduboy2NoUSB
+{
+  friend int main();
+
+  private:
+    static void mainNoUSB();
+};
+
 
 /** \brief
  * Lower level functions generally dealing directly with the hardware.
@@ -322,7 +332,7 @@ int main() { \
  * that this may eliminate the need to create an entire local copy of the
  * library, in order to extend the functionality, in most circumstances.
  */
-class Arduboy2Core
+class Arduboy2Core : public Arduboy2NoUSB
 {
   friend class Arduboy2Ex;
 
@@ -828,11 +838,6 @@ class Arduboy2Core
      */
     static void exitToBootloader();
 
-    // Replacement main() that eliminates the USB stack code.
-    // Used by the ARDUBOY_NO_USB macro. This should not be called
-    // directly from a sketch.
-    static void mainNoUSB();
-
   protected:
     // internals
     static void setCPUSpeed8MHz();