diff --git a/source/third_party/ogre3d_preprocessor/OgreGLSLPreprocessor.h b/source/third_party/ogre3d_preprocessor/OgreGLSLPreprocessor.h
index 29b949257c..33847d880d 100644
--- a/source/third_party/ogre3d_preprocessor/OgreGLSLPreprocessor.h
+++ b/source/third_party/ogre3d_preprocessor/OgreGLSLPreprocessor.h
@@ -168,7 +168,7 @@ namespace Ogre
             void SetValue (long iValue);
 
             /// Test two tokens for equality
-            bool operator == (const Token &iOther)
+            bool operator == (const Token &iOther) const
             {
                 if (iOther.Length != Length)
                     return false;