diff --git a/glm/gtx/log_base.hpp b/glm/gtx/log_base.hpp
index 94d03472..b56ab009 100644
--- a/glm/gtx/log_base.hpp
+++ b/glm/gtx/log_base.hpp
@@ -57,8 +57,8 @@ namespace glm
 	//! From GLM_GTX_log_base.
 	template <typename genType>
 	GLM_FUNC_DECL genType log(
-		genType x,
-		genType base);
+		genType const & x,
+		genType const & base);
 
 	//! Logarithm for any base.
 	//! From GLM_GTX_log_base.