diff --git a/glm/core/func_integer.inl b/glm/core/func_integer.inl
index 07a748ba..62d5b920 100644
--- a/glm/core/func_integer.inl
+++ b/glm/core/func_integer.inl
@@ -544,10 +544,13 @@ namespace glm
 	)
 	{
 		/**
-		 * ctz returns the number or trailing 0-bits; see
+		 * clz returns the number or trailing 0-bits; see
 		 * http://gcc.gnu.org/onlinedocs/gcc-4.7.1/gcc/Other-Builtins.html
+		 *
+		 * NoteBecause __builtin_clz only works for unsigned ints, this
+		 * implementation will not work for 64-bit integers.
 		 */
-		return __builtin_ctz(Value);
+		return 31 - __builtin_clz(Value);
 	}
 
 #else