diff --git a/src/Core/Materials/OOShaderMaterial.m b/src/Core/Materials/OOShaderMaterial.m
index 457f8e7f..9dba2a25 100644
--- a/src/Core/Materials/OOShaderMaterial.m
+++ b/src/Core/Materials/OOShaderMaterial.m
@@ -260,13 +260,19 @@ static NSString *MacrosToString(NSDictionary *macros);
 	if (OK)
 	{
 		// write gloss and index of refraction to the uniforms dictionary
-
-		float gloss = OOClamp_0_1_f([configuration oo_floatForKey:@"gloss"  defaultValue:0.5f]);
-		[self setUniform:@"uGloss" floatValue:gloss];
 		
-		float ior = [configuration oo_floatForKey:@"ior"  defaultValue:1.0f];
-		if (ior <= 0.0f)  ior = 0.001f;
-		[self setUniform:@"uIOR" floatValue:ior];
+		if (![uniforms objectForKey:@"uGloss"])
+		{
+			float gloss = OOClamp_0_1_f([configuration oo_floatForKey:@"gloss"  defaultValue:0.5f]);
+			[self setUniform:@"uGloss" floatValue:gloss];
+		}
+		
+		if (![uniforms objectForKey:@"uIOR"])
+		{
+			float ior = [configuration oo_floatForKey:@"ior"  defaultValue:1.0f];
+			if (ior <= 0.0f)  ior = 0.001f;
+			[self setUniform:@"uIOR" floatValue:ior];
+		}
 	}
 	
 	if (!OK)