diff --git a/source/blender/python/mathutils/mathutils.c b/source/blender/python/mathutils/mathutils.c
index 28b9cfaae57f..5dddf0c760f6 100644
--- a/source/blender/python/mathutils/mathutils.c
+++ b/source/blender/python/mathutils/mathutils.c
@@ -442,7 +442,7 @@ unsigned char Mathutils_RegisterCallback(Mathutils_Callback *cb)
 			return i;
 	}
 
-	BLI_assert(i + 1 < MATHUTILS_TOT_CB);
+	BLI_assert(i < MATHUTILS_TOT_CB);
 
 	mathutils_callbacks[i] = cb;
 	return i;