diff --git a/neo/renderer/Image_program.cpp b/neo/renderer/Image_program.cpp
index 08effdde..0eeb3111 100644
--- a/neo/renderer/Image_program.cpp
+++ b/neo/renderer/Image_program.cpp
@@ -185,6 +185,24 @@ static void R_InvertAlpha( byte* data, int width, int height )
 	}
 }
 
+/*
+=================
+R_InvertGreen
+=================
+*/
+static void R_InvertGreen( byte* data, int width, int height )
+{
+	int		i;
+	int		c;
+
+	c = width * height * 4;
+
+	for( i = 0 ; i < c ; i += 4 )
+	{
+		data[i + 1] = 255 - data[i + 1];
+	}
+}
+
 /*
 =================
 R_InvertColor
@@ -608,6 +626,23 @@ static bool R_ParseImageProgram_r( idLexer& src, byte** pic, int* width, int* he
 		return true;
 	}
 
+	// RB: invertGreen to allow flipping the Y-Axis of normal maps
+	if( !token.Icmp( "invertGreen" ) )
+	{
+		MatchAndAppendToken( src, "(" );
+
+		R_ParseImageProgram_r( src, pic, width, height, timestamps, usage );
+
+		// process it
+		if( pic )
+		{
+			R_InvertGreen( *pic, *width, *height );
+		}
+
+		MatchAndAppendToken( src, ")" );
+		return true;
+	}
+
 	if( !token.Icmp( "invertColor" ) )
 	{
 		MatchAndAppendToken( src, "(" );