diff --git a/platform/base_glsl.pk3dir/glsl/unlit.glsl b/platform/base_glsl.pk3dir/glsl/unlit.glsl
index 276fcbcd..266c38ba 100644
--- a/platform/base_glsl.pk3dir/glsl/unlit.glsl
+++ b/platform/base_glsl.pk3dir/glsl/unlit.glsl
@@ -26,6 +26,13 @@ void main ()
 void main ()
 {
 	vec4 d_f = texture2D( s_diffuse, tex_c );
+
+#ifdef MASK
+		// alpha-testing happens here
+		if (d_f.a < MASK)
+			discard;
+#endif
+
 	gl_FragColor = fog4( d_f );
 }
 #endif