diff --git a/include/osg/GL2Extensions b/include/osg/GL2Extensions
index 16b5f0bab..2d4525ae3 100644
--- a/include/osg/GL2Extensions
+++ b/include/osg/GL2Extensions
@@ -129,7 +129,12 @@ typedef char GLchar;
 
 #if !defined(GL_SAMPLER_1D)
 #define GL_SAMPLER_1D                     0x8B5D
+#endif
+#if !defined(GL_SAMPLER_3D)
 #define GL_SAMPLER_3D                     0x8B5F
+#endif
+
+#if !defined(GL_SAMPLER_1D_SHADOW)
 #define GL_SAMPLER_1D_SHADOW              0x8B61
 #define GL_SAMPLER_2D_SHADOW              0x8B62
 #endif