diff --git a/code/renderergl1/tr_shader.c b/code/renderergl1/tr_shader.c
index 525ac3c2..c931326f 100644
--- a/code/renderergl1/tr_shader.c
+++ b/code/renderergl1/tr_shader.c
@@ -1568,6 +1568,23 @@ static qboolean ParseShader( char **text )
 				return qfalse;
 			}
 
+			if ( r_greyscale->integer )
+			{
+				float luminance;
+
+				luminance = LUMA( shader.fogParms.color[0], shader.fogParms.color[1], shader.fogParms.color[2] );
+				VectorSet( shader.fogParms.color, luminance, luminance, luminance );
+			}
+			else if ( r_greyscale->value )
+			{
+				float luminance;
+
+				luminance = LUMA( shader.fogParms.color[0], shader.fogParms.color[1], shader.fogParms.color[2] );
+				shader.fogParms.color[0] = LERP( shader.fogParms.color[0], luminance, r_greyscale->value );
+				shader.fogParms.color[1] = LERP( shader.fogParms.color[1], luminance, r_greyscale->value );
+				shader.fogParms.color[2] = LERP( shader.fogParms.color[2], luminance, r_greyscale->value );
+			}
+
 			token = COM_ParseExt( text, qfalse );
 			if ( !token[0] ) 
 			{
diff --git a/code/renderergl2/tr_shader.c b/code/renderergl2/tr_shader.c
index 8d7ed540..9bf2ec20 100644
--- a/code/renderergl2/tr_shader.c
+++ b/code/renderergl2/tr_shader.c
@@ -1856,6 +1856,23 @@ static qboolean ParseShader( char **text )
 				return qfalse;
 			}
 
+			if ( r_greyscale->integer )
+			{
+				float luminance;
+
+				luminance = LUMA( shader.fogParms.color[0], shader.fogParms.color[1], shader.fogParms.color[2] );
+				VectorSet( shader.fogParms.color, luminance, luminance, luminance );
+			}
+			else if ( r_greyscale->value )
+			{
+				float luminance;
+
+				luminance = LUMA( shader.fogParms.color[0], shader.fogParms.color[1], shader.fogParms.color[2] );
+				shader.fogParms.color[0] = LERP( shader.fogParms.color[0], luminance, r_greyscale->value );
+				shader.fogParms.color[1] = LERP( shader.fogParms.color[1], luminance, r_greyscale->value );
+				shader.fogParms.color[2] = LERP( shader.fogParms.color[2], luminance, r_greyscale->value );
+			}
+
 			token = COM_ParseExt( text, qfalse );
 			if ( !token[0] ) 
 			{