diff --git a/src/gl/renderer/gl_2ddrawer.cpp b/src/gl/renderer/gl_2ddrawer.cpp
index cda4ea374..9c89c6f60 100644
--- a/src/gl/renderer/gl_2ddrawer.cpp
+++ b/src/gl/renderer/gl_2ddrawer.cpp
@@ -91,7 +91,9 @@ void F2DDrawer::AddTexture(FTexture *img, DrawParms &parms)
 
 	if (!img->bHasCanvas)
 	{
-		if (!parms.alphaChannel)
+		dg.mAlphaTexture = !!(parms.style.Flags & STYLEF_RedIsAlpha);
+
+		if (!dg.mAlphaTexture)
 		{
 			if (parms.remap != NULL && !parms.remap->Inactive)
 			{
@@ -99,7 +101,6 @@ void F2DDrawer::AddTexture(FTexture *img, DrawParms &parms)
 				if (pal) dg.mTranslation = -pal->GetIndex();
 			}
 		}
-		dg.mAlphaTexture = !!(parms.style.Flags & STYLEF_RedIsAlpha);
 		u1 = gltex->GetUL();
 		v1 = gltex->GetVT();
 		u2 = gltex->GetUR();
diff --git a/src/gl/renderer/gl_renderstate.h b/src/gl/renderer/gl_renderstate.h
index 09888db5c..4e844c979 100644
--- a/src/gl/renderer/gl_renderstate.h
+++ b/src/gl/renderer/gl_renderstate.h
@@ -144,14 +144,9 @@ public:
 
 	void SetMaterial(FMaterial *mat, int clampmode, int translation, int overrideshader, bool alphatexture)
 	{
-		// textures without their own palette are a special case for use as an alpha texture:
-		// They use the color index directly as an alpha value instead of using the palette's red.
-		// To handle this case, we need to set a special translation for such textures.
-		// Without shaders this translation must be applied to any texture.
-		if (alphatexture)
-		{
-			if (mat->tex->UseBasePalette() || gl.legacyMode) translation = TRANSLATION(TRANSLATION_Standard, 8);
-		}
+		// alpha textures need special treatment in the legacy renderer because withouz shaders they need a different texture.
+		if (alphatexture &&  gl.legacyMode) translation = TRANSLATION(TRANSLATION_Standard, 8);
+		
 		if (mat->tex->bHasCanvas)
 		{
 			mTempTM = TM_OPAQUE;
diff --git a/src/textures/textures.h b/src/textures/textures.h
index 0c175f328..c0a1e9dcf 100644
--- a/src/textures/textures.h
+++ b/src/textures/textures.h
@@ -211,6 +211,7 @@ public:
 		TEX_Flat,
 		TEX_Sprite,
 		TEX_WallPatch,
+		TEX_Build,		// no longer used but needs to remain for ZScript
 		TEX_SkinSprite,
 		TEX_Decal,
 		TEX_MiscPatch,
diff --git a/wadsrc/static/shaders/glsl/main.fp b/wadsrc/static/shaders/glsl/main.fp
index 444a9811f..2ff3ef483 100644
--- a/wadsrc/static/shaders/glsl/main.fp
+++ b/wadsrc/static/shaders/glsl/main.fp
@@ -64,7 +64,8 @@ vec4 getTexel(vec2 st)
 			break;
 			
 		case 4:	// TM_REDTOALPHA
-			texel = vec4(1.0, 1.0, 1.0, texel.r*texel.a);
+			float gray = (texel.r * 0.3 + texel.g * 0.56 + texel.b * 0.14);	
+			texel = vec4(1.0, 1.0, 1.0, gray*texel.a);
 			break;
 			
 		case 5:	// TM_CLAMPY