diff --git a/olcPixelGameEngine.h b/olcPixelGameEngine.h
index 5e59a87a..b581a01b 100644
--- a/olcPixelGameEngine.h
+++ b/olcPixelGameEngine.h
@@ -594,6 +594,7 @@ namespace X11
 #include <GL/freeglut_ext.h>
 #endif
 #if defined(__APPLE__)
+#include <assert.h>
 #include <GLUT/glut.h>
 #include <objc/message.h>
 #include <objc/NSObjCRuntime.h>
@@ -8112,3 +8113,4 @@ namespace olc
 // | END OF OLC_PGE_APPLICATION                                                   |
 // O------------------------------------------------------------------------------O
 
+