diff --git a/Makefile b/Makefile
index ea3bb71..5b6999d 100644
--- a/Makefile
+++ b/Makefile
@@ -116,7 +116,7 @@ LD = cc
 CFLAGS.EXTRA = -dynamic -I/usr/X11R6/include
 LDFLAGS.SO = -dynamiclib
 LDFLAGS.EXTRA = -L/usr/X11R6/lib
-ifdef GLEW_APPLE_GLX
+ifneq (undefined, $(origin GLEW_APPLE_GLX))
 CFLAGS.EXTRA += -D'GLEW_APPLE_GLX'
 LDFLAGS.GL = -lXmu -lXi -lGLU -lGL -lXext -lX11
 else
diff --git a/auto/src/glew_glx.c b/auto/src/glew_glx.c
index cecb0b9..aba4b0d 100644
--- a/auto/src/glew_glx.c
+++ b/auto/src/glew_glx.c
@@ -1,7 +1,7 @@
   return GLEW_OK;
 }
 
-#else /* _UNIX */
+#elif !defined(__APPLE__) || defined(GLEW_APPLE_GLX) /* _UNIX */
 
 GLboolean glxewGetExtension (const GLubyte *name)
 {