diff --git a/include/QF/mathlib.h b/include/QF/mathlib.h
index d78e281e6..e657522c6 100644
--- a/include/QF/mathlib.h
+++ b/include/QF/mathlib.h
@@ -149,7 +149,10 @@ R_CullBox (const vec3_t mins, const vec3_t maxs)
 	return false;
 }
 
-extern inline qboolean
+#ifndef IMPLEMENT_R_CullSphere
+extern inline
+#endif
+qboolean
 R_CullSphere (const vec3_t origin, const float radius)
 {
 	int		i;
diff --git a/libs/util/mathlib.c b/libs/util/mathlib.c
index 92093b1ef..38fa2fe2a 100644
--- a/libs/util/mathlib.c
+++ b/libs/util/mathlib.c
@@ -40,6 +40,7 @@ static const char rcsid[] =
 #include <math.h>
 
 #define IMPLEMENT_R_CullBox
+#define IMPLEMENT_R_CullSphere
 
 #include "QF/mathlib.h"
 #include "QF/qtypes.h"