diff --git a/src/gl/renderer/gl_renderstate.cpp b/src/gl/renderer/gl_renderstate.cpp
index 7f5fd3b0d..673c201b8 100644
--- a/src/gl/renderer/gl_renderstate.cpp
+++ b/src/gl/renderer/gl_renderstate.cpp
@@ -125,7 +125,7 @@ bool FRenderState::ApplyShader()
 	if (gl.hasGLSL())
 	{
 		FShader *activeShader;
-		if (mSpecialEffect > 0)
+		if (mSpecialEffect > EFF_NONE)
 		{
 			activeShader = GLRenderer->mShaderManager->BindEffect(mSpecialEffect);
 		}
@@ -151,7 +151,7 @@ bool FRenderState::ApplyShader()
 
 		glColor4fv(mColor.vec);
 
-		activeShader->muDesaturation.Set(mDesaturation);
+		activeShader->muDesaturation.Set(mDesaturation / 255.f);
 		activeShader->muFogEnabled.Set(fogset);
 		activeShader->muTextureMode.Set(mTextureMode);
 		activeShader->muCameraPos.Set(mCameraPos.vec);
diff --git a/wadsrc/static/shaders/glsl/main.fp b/wadsrc/static/shaders/glsl/main.fp
index db5b8cb19..35b355206 100644
--- a/wadsrc/static/shaders/glsl/main.fp
+++ b/wadsrc/static/shaders/glsl/main.fp
@@ -31,8 +31,13 @@ vec4 desaturate(vec4 texel)
 {
 	if (uDesaturationFactor > 0.0)
 	{
-		float gray = (texel.r * 0.3 + texel.g * 0.56 + texel.b * 0.14);	
-		return mix (vec4(gray,gray,gray,texel.a), texel, uDesaturationFactor);
+		float gray = (texel.r * 0.3 + texel.g * 0.56 + texel.b * 0.14) * uDesaturationFactor;	
+		
+		vec4 desaturated = vec4(gray,gray,gray,texel.a);
+		// I have absolutely no idea why this works and 'mix' doesn't...
+		texel *= (1.0-uDesaturationFactor);
+		return texel + desaturated;
+		//return mix (desaturated, texel, uDesaturationFactor);
 	}
 	else
 	{