diff --git a/plugins/GSdx/res/glsl/convert.glsl b/plugins/GSdx/res/glsl/convert.glsl
index f3ef9887b6..0ed4b16a18 100644
--- a/plugins/GSdx/res/glsl/convert.glsl
+++ b/plugins/GSdx/res/glsl/convert.glsl
@@ -77,7 +77,7 @@ layout(std140, binding = 15) uniform cb15
 
 vec4 sample_c()
 {
-    return texture(TextureSampler, PSin_t );
+    return texture(TextureSampler, PSin_t);
 }
 
 vec4 ps_crt(uint i)
@@ -372,11 +372,7 @@ void ps_main3()
 #ifdef ps_main4
 void ps_main4()
 {
-    // FIXME mod and fmod are different when value are negative
-    // 	output.c = fmod(sample_c(input.t) * 255 + 0.5f, 256) / 255;
-    vec4 c = mod(sample_c() * 255.0f + 0.5f, 256.0f) / 255.0f;
-
-    SV_Target0 = c;
+    SV_Target0 = mod(round(sample_c() * 255.0f), 256.0f) / 255.0f;
 }
 #endif
 
diff --git a/plugins/GSdx/res/glsl_source.h b/plugins/GSdx/res/glsl_source.h
index dbe510afdf..d56238466c 100644
--- a/plugins/GSdx/res/glsl_source.h
+++ b/plugins/GSdx/res/glsl_source.h
@@ -102,7 +102,7 @@ static const char* convert_glsl =
 	"\n"
 	"vec4 sample_c()\n"
 	"{\n"
-	"    return texture(TextureSampler, PSin_t );\n"
+	"    return texture(TextureSampler, PSin_t);\n"
 	"}\n"
 	"\n"
 	"vec4 ps_crt(uint i)\n"
@@ -397,11 +397,7 @@ static const char* convert_glsl =
 	"#ifdef ps_main4\n"
 	"void ps_main4()\n"
 	"{\n"
-	"    // FIXME mod and fmod are different when value are negative\n"
-	"    // 	output.c = fmod(sample_c(input.t) * 255 + 0.5f, 256) / 255;\n"
-	"    vec4 c = mod(sample_c() * 255.0f + 0.5f, 256.0f) / 255.0f;\n"
-	"\n"
-	"    SV_Target0 = c;\n"
+	"    SV_Target0 = mod(round(sample_c() * 255.0f), 256.0f) / 255.0f;\n"
 	"}\n"
 	"#endif\n"
 	"\n"