diff --git a/wadsrc/static/shaders/lightmap/frag_blur.glsl b/wadsrc/static/shaders/lightmap/frag_blur.glsl
index 8dbb3069b..b51561081 100644
--- a/wadsrc/static/shaders/lightmap/frag_blur.glsl
+++ b/wadsrc/static/shaders/lightmap/frag_blur.glsl
@@ -4,20 +4,29 @@ layout(set = 0, binding = 0) uniform sampler2D tex;
 layout(location = 0) in vec3 worldpos;
 layout(location = 0) out vec4 fragcolor;
 
+vec4 centerFragColor;
+
+vec4 clampedSample(vec4 f)
+{
+	return f != vec4(0, 0, 0, 0) ? f : centerFragColor;
+}
+
 void main()
 {
 	ivec2 size = textureSize(tex, 0);
 	vec2 texCoord = gl_FragCoord.xy / vec2(size);
 
+	centerFragColor = textureOffset(tex, texCoord, ivec2(0, 0));
+
 #if defined(BLUR_HORIZONTAL)
 	fragcolor =
-		textureOffset(tex, texCoord, ivec2( 0, 0)) * 0.5 +
-		textureOffset(tex, texCoord, ivec2( 1, 0)) * 0.25 +
-		textureOffset(tex, texCoord, ivec2(-1, 0)) * 0.25;
+		centerFragColor * 0.5 +
+		clampedSample(textureOffset(tex, texCoord, ivec2( 1, 0))) * 0.25 +
+		clampedSample(textureOffset(tex, texCoord, ivec2(-1, 0))) * 0.25;
 #else
 	fragcolor =
-		textureOffset(tex, texCoord, ivec2(0, 0)) * 0.5 +
-		textureOffset(tex, texCoord, ivec2(0, 1)) * 0.25 +
-		textureOffset(tex, texCoord, ivec2(0,-1)) * 0.25;
+		centerFragColor * 0.5 +
+		clampedSample(textureOffset(tex, texCoord, ivec2(0, 1))) * 0.25 +
+		clampedSample(textureOffset(tex, texCoord, ivec2(0,-1))) * 0.25;
 #endif
 }