diff --git a/simgear/scene/model/SGMaterialAnimation.cxx b/simgear/scene/model/SGMaterialAnimation.cxx
index 72df88e5..1e7afdd9 100644
--- a/simgear/scene/model/SGMaterialAnimation.cxx
+++ b/simgear/scene/model/SGMaterialAnimation.cxx
@@ -98,7 +98,7 @@ struct ColorSpec {
     return v;
   }
 
-  osg::Vec4& rgbaVec4()
+  osg::Vec4 rgbaVec4()
   {
     return rgba().osg();
   }