diff --git a/wadsrc/static/shaders/glsl/main.fp b/wadsrc/static/shaders/glsl/main.fp
index faa2ff0e3..b10c99a17 100644
--- a/wadsrc/static/shaders/glsl/main.fp
+++ b/wadsrc/static/shaders/glsl/main.fp
@@ -141,8 +141,8 @@ float R_DoomLightingEquation(float light)
 
 	/* The zdoom light equation */
 	float vis = globVis / z;
-	float shade = 64.0 - (L + 12) * 32.0/128.0;
-	float lightscale = clamp((shade - min(24.0, vis)) / 32.0, 0.0, 31/32.0);
+	float shade = 64.0 - (L + 12.0) * 32.0/128.0;
+	float lightscale = clamp((shade - min(24.0, vis)) / 32.0, 0.0, 31.0/32.0);
 
 	// Result is the normalized colormap index (0 bright .. 1 dark)
 	return lightscale;