diff --git a/glm/gtc/quaternion.hpp b/glm/gtc/quaternion.hpp
index daf9cc19..5a4425e6 100644
--- a/glm/gtc/quaternion.hpp
+++ b/glm/gtc/quaternion.hpp
@@ -134,8 +134,8 @@ namespace glm
 
 		/// Explicit conversion operators
 #		if GLM_HAS_EXPLICIT_CONVERSION_OPERATORS
-			GLM_FUNC_DECL explicit operator tmat3x3<T, P>();
-			GLM_FUNC_DECL explicit operator tmat4x4<T, P>();
+			GLM_FUNC_DECL explicit operator tmat3x3<T, P>() const;
+			GLM_FUNC_DECL explicit operator tmat4x4<T, P>() const;
 #		endif
 
 		/// Create a quaternion from two normalized axis
diff --git a/glm/gtc/quaternion.inl b/glm/gtc/quaternion.inl
index e5fe5505..75ef41ee 100644
--- a/glm/gtc/quaternion.inl
+++ b/glm/gtc/quaternion.inl
@@ -265,13 +265,13 @@ namespace detail
 
 #	if GLM_HAS_EXPLICIT_CONVERSION_OPERATORS
 	template <typename T, precision P>
-	GLM_FUNC_QUALIFIER tquat<T, P>::operator tmat3x3<T, P>()
+	GLM_FUNC_QUALIFIER tquat<T, P>::operator tmat3x3<T, P>() const
 	{
 		return mat3_cast(*this);
 	}
 	
 	template <typename T, precision P>	
-	GLM_FUNC_QUALIFIER tquat<T, P>::operator tmat4x4<T, P>()
+	GLM_FUNC_QUALIFIER tquat<T, P>::operator tmat4x4<T, P>() const
 	{
 		return mat4_cast(*this);
 	}