diff --git a/RenderSystems/GL3Plus/include/GLSL/OgreGLSLPreprocessor.h b/RenderSystems/GL3Plus/include/GLSL/OgreGLSLPreprocessor.h
index 9d5c47f6160..a21b7c1b2ba 100644
--- a/RenderSystems/GL3Plus/include/GLSL/OgreGLSLPreprocessor.h
+++ b/RenderSystems/GL3Plus/include/GLSL/OgreGLSLPreprocessor.h
@@ -521,6 +521,16 @@ namespace Ogre
          */
         char *Parse( const char *iSource, size_t iLength, size_t &oLength );
 
+        /** Parse the input string as a preamble (i.e. to define a lot of enums).
+        @param iSource
+            The source text containing preamble macros.
+        @param iLength
+            The length of iSource text in characters.
+        @return
+            False on errors. True on success.
+        */
+        bool ParsePreamble( const char *iSource, size_t iLength );
+
         /**
          * An error handler function type.
          * The default implementation just drops a note to stderr and
diff --git a/RenderSystems/GL3Plus/src/GLSL/OgreGLSLPreprocessor.cpp b/RenderSystems/GL3Plus/src/GLSL/OgreGLSLPreprocessor.cpp
index dbcb6845a73..5dbd8c55172 100644
--- a/RenderSystems/GL3Plus/src/GLSL/OgreGLSLPreprocessor.cpp
+++ b/RenderSystems/GL3Plus/src/GLSL/OgreGLSLPreprocessor.cpp
@@ -1437,4 +1437,10 @@ namespace Ogre
         return retval.Buffer;
     }
 
+    bool CPreprocessor::ParsePreamble( const char *iSource, size_t iLength )
+    {
+        Token retval = Parse( Token( Token::TK_TEXT, iSource, iLength ) );
+        return retval.Type != Token::TK_ERROR;
+    }
+
 }  // namespace Ogre
diff --git a/RenderSystems/GL3Plus/src/GLSL/OgreGLSLShader.cpp b/RenderSystems/GL3Plus/src/GLSL/OgreGLSLShader.cpp
index 8cf99c165de..53cf2ade1b6 100644
--- a/RenderSystems/GL3Plus/src/GLSL/OgreGLSLShader.cpp
+++ b/RenderSystems/GL3Plus/src/GLSL/OgreGLSLShader.cpp
@@ -163,7 +163,6 @@ namespace Ogre
             replaceVersionMacros();
 
         // Mask out vulkan_layout() macros
-        size_t unusedVal = 0;
         const String preamble =
             "#define vulkan_layout(x)\n"
             "#define vulkan( x )\n"
@@ -180,7 +179,7 @@ namespace Ogre
             "#define vkSampler2DArray( a, b ) a\n"
             "#define vkSampler3D( a, b ) a\n"
             "#define vkSamplerCube( a, b ) a\n";
-        cpp.Parse( preamble.c_str(), preamble.size(), unusedVal );
+        cpp.ParsePreamble( preamble.c_str(), preamble.size() );
 
         // Pass all user-defined macros to preprocessor
         if( !mPreprocessorDefines.empty() )