diff --git a/qglview/gltypes.h b/qglview/gltypes.h
index 220a75e..e090da0 100644
--- a/qglview/gltypes.h
+++ b/qglview/gltypes.h
@@ -110,11 +110,15 @@ typedef QGLShaderProgram __GLShaderProgram__;
 #  define GL_TEXTURE_MAX_ANISOTROPY_EXT 0x84FE
 #endif
 
-#ifdef CC_VC
+#ifndef M_PI
 #  define M_PI 3.14159265358979323846
 #endif
-#define M_2PI 6.28318530717958647692
-#define M_PI_3 1.04719755119659774615
+#ifndef M_2PI
+#  define M_2PI 6.28318530717958647692
+#endif
+#ifndef M_PI_3
+#  define M_PI_3 1.04719755119659774615
+#endif
 
 #ifndef GL_RGBA16F
 #  define GL_RGBA16F GL_RGBA16F_ARB