diff --git a/src/gl/dynlights/gl_shadowmap.cpp b/src/gl/dynlights/gl_shadowmap.cpp
index b70304db0a..005f38ad8c 100644
--- a/src/gl/dynlights/gl_shadowmap.cpp
+++ b/src/gl/dynlights/gl_shadowmap.cpp
@@ -83,7 +83,7 @@ void FShadowMap::UploadLights()
 		ADynamicLight *light = it.Next();
 		if (!light) break;
 
-		mLightToShadowmap[light] = mLights.Size();
+		mLightToShadowmap[light] = mLights.Size() / 4;
 
 		mLights.Push(light->X());
 		mLights.Push(light->Y());
diff --git a/wadsrc/static/shaders/glsl/main.fp b/wadsrc/static/shaders/glsl/main.fp
index 0d4cf0607e..e986f65f0a 100644
--- a/wadsrc/static/shaders/glsl/main.fp
+++ b/wadsrc/static/shaders/glsl/main.fp
@@ -158,7 +158,9 @@ float shadowmapAttenuation(vec4 lightpos, float shadowIndex)
 		else
 			u = dir.x / dir.y * 0.125 + (0.50 + 0.125);
 	}
-	return texture(ShadowMap, vec2(u, v)).x < dot(dir, dir) ? 1.0 : 0.0;
+	dir -= sign(dir); // margin, to remove wall acne
+	float dist2 = dot(dir, dir);
+	return texture(ShadowMap, vec2(u, v)).x > dist2 ? 1.0 : 0.0;
 }
 
 //===========================================================================
diff --git a/wadsrc/static/shaders/glsl/shadowmap.fp b/wadsrc/static/shaders/glsl/shadowmap.fp
index 1c9b3a754b..957e08b77f 100644
--- a/wadsrc/static/shaders/glsl/shadowmap.fp
+++ b/wadsrc/static/shaders/glsl/shadowmap.fp
@@ -129,8 +129,8 @@ void main()
 		{
 		case 0: pixelpos = vec2((gl_FragCoord.x - 128.0) / 128.0, 1.0); break;
 		case 1: pixelpos = vec2(1.0, (gl_FragCoord.x - 384.0) / 128.0); break;
-		case 2: pixelpos = vec2((gl_FragCoord.x - 640.0) / 128.0, -1.0); break;
-		case 3: pixelpos = vec2(-1.0, (gl_FragCoord.x - 896.0) / 128.0); break;
+		case 2: pixelpos = vec2(-(gl_FragCoord.x - 640.0) / 128.0, -1.0); break;
+		case 3: pixelpos = vec2(-1.0, -(gl_FragCoord.x - 896.0) / 128.0); break;
 		}
 		pixelpos = lightpos + pixelpos * radius;