diff --git a/glm/gtc/packing.inl b/glm/gtc/packing.inl
index 332840bd..032ecd88 100644
--- a/glm/gtc/packing.inl
+++ b/glm/gtc/packing.inl
@@ -554,11 +554,13 @@ namespace detail
 
 	GLM_FUNC_QUALIFIER uint32 packSnorm3x10_1x2(vec4 const & v)
 	{
+		ivec4 const Pack(round(clamp(v,-1.0f, 1.0f) * vec4(511.f, 511.f, 511.f, 1.f)));
+
 		detail::i10i10i10i2 Result;
-		Result.data.x = int(round(clamp(v.x,-1.0f, 1.0f) * 511.f));
-		Result.data.y = int(round(clamp(v.y,-1.0f, 1.0f) * 511.f));
-		Result.data.z = int(round(clamp(v.z,-1.0f, 1.0f) * 511.f));
-		Result.data.w = int(round(clamp(v.w,-1.0f, 1.0f) *   1.f));
+		Result.data.x = Pack.x;
+		Result.data.y = Pack.y;
+		Result.data.z = Pack.z;
+		Result.data.w = Pack.w;
 		return Result.pack;
 	}
 
@@ -566,12 +568,10 @@ namespace detail
 	{
 		detail::i10i10i10i2 Unpack;
 		Unpack.pack = v;
-		vec4 Result;
-		Result.x = clamp(float(Unpack.data.x) / 511.f, -1.0f, 1.0f);
-		Result.y = clamp(float(Unpack.data.y) / 511.f, -1.0f, 1.0f);
-		Result.z = clamp(float(Unpack.data.z) / 511.f, -1.0f, 1.0f);
-		Result.w = clamp(float(Unpack.data.w) /   1.f, -1.0f, 1.0f);
-		return Result;
+
+		vec4 const Result(Unpack.data.x, Unpack.data.y, Unpack.data.z, Unpack.data.w);
+
+		return clamp(Result * vec4(1.f / 511.f, 1.f / 511.f, 1.f / 511.f, 1.f), -1.0f, 1.0f);
 	}
 
 	GLM_FUNC_QUALIFIER uint32 packUnorm3x10_1x2(vec4 const & v)
diff --git a/readme.md b/readme.md
index f7c91f97..74cd6463 100644
--- a/readme.md
+++ b/readme.md
@@ -62,6 +62,7 @@ glm::mat4 camera(float Translate, glm::vec2 const & Rotate)
 #### Improvements:
 - Added lowp variant of GTC_colorspace convertLinearToSRGB #419
 - Replaced the manual by a markdown version #458
+- Optimized GTC_packing implementation
 
 #### Fixes:
 - Removed doxygen references to GTC_half_float which was removed in 0.9.4
diff --git a/test/gtc/gtc_packing.cpp b/test/gtc/gtc_packing.cpp
index 4e309aa5..0229dfd3 100644
--- a/test/gtc/gtc_packing.cpp
+++ b/test/gtc/gtc_packing.cpp
@@ -690,10 +690,10 @@ int main()
 	Error += test_RGBM();
 
 // It looks like GLM has a but that travis CI shows in this configuration #577
-#if !((GLM_ARCH == GLM_ARCH_PURE) && (GLM_COMPILER & GLM_COMPILER_GCC))
+//#if !((GLM_ARCH == GLM_ARCH_PURE) && (GLM_COMPILER & GLM_COMPILER_GCC))
 	Error += test_Unorm3x10_1x2();
-#endif
 	Error += test_Snorm3x10_1x2();
+//#endif
 
 	Error += test_I3x10_1x2();
 	Error += test_U3x10_1x2();