diff --git a/src/Gui/GLBuffer.cpp b/src/Gui/GLBuffer.cpp
index a218073730..dc6b9d617a 100644
--- a/src/Gui/GLBuffer.cpp
+++ b/src/Gui/GLBuffer.cpp
@@ -24,7 +24,9 @@
 #include "PreCompiled.h"
 
 #ifndef FC_OS_WIN32
-#define GL_GLEXT_PROTOTYPES
+# ifndef GL_GLEXT_PROTOTYPES
+# define GL_GLEXT_PROTOTYPES 1
+# endif
 #endif
 
 #ifdef FC_OS_MACOSX
diff --git a/src/Mod/Mesh/Gui/SoFCIndexedFaceSet.cpp b/src/Mod/Mesh/Gui/SoFCIndexedFaceSet.cpp
index 7c7a7ebde8..8b0f9a5e1a 100644
--- a/src/Mod/Mesh/Gui/SoFCIndexedFaceSet.cpp
+++ b/src/Mod/Mesh/Gui/SoFCIndexedFaceSet.cpp
@@ -24,7 +24,9 @@
 #include "PreCompiled.h"
 
 #ifndef FC_OS_WIN32
-#define GL_GLEXT_PROTOTYPES
+# ifndef GL_GLEXT_PROTOTYPES
+# define GL_GLEXT_PROTOTYPES 1
+# endif
 #endif
 
 #ifndef _PreComp_
diff --git a/src/Mod/Part/Gui/SoBrepFaceSet.cpp b/src/Mod/Part/Gui/SoBrepFaceSet.cpp
index 441a9c695a..8c0c17c977 100644
--- a/src/Mod/Part/Gui/SoBrepFaceSet.cpp
+++ b/src/Mod/Part/Gui/SoBrepFaceSet.cpp
@@ -23,7 +23,9 @@
 #include "PreCompiled.h"
 
 #ifndef FC_OS_WIN32
-#define GL_GLEXT_PROTOTYPES
+# ifndef GL_GLEXT_PROTOTYPES
+# define GL_GLEXT_PROTOTYPES 1
+# endif
 #endif
 
 #ifndef _PreComp_