diff --git a/src/osg/ColorMaski.cpp b/src/osg/ColorMaski.cpp
index 1cae24a92..61e7c4f89 100644
--- a/src/osg/ColorMaski.cpp
+++ b/src/osg/ColorMaski.cpp
@@ -39,7 +39,7 @@ void ColorMaski::apply(State& state) const
     const GLExtensions* extensions = state.get<GLExtensions>();
     if (extensions->glColorMaski)
     {
-        extensions->glColorMaski((GLboolean)_index, (GLboolean)_red,(GLboolean)_green,(GLboolean)_blue,(GLboolean)_alpha);
+        extensions->glColorMaski((GLuint)_index, (GLboolean)_red,(GLboolean)_green,(GLboolean)_blue,(GLboolean)_alpha);
     }
     else
     {