diff --git a/glm/ext/quaternion_common.hpp b/glm/ext/quaternion_common.hpp
index a2a43463..f738692a 100644
--- a/glm/ext/quaternion_common.hpp
+++ b/glm/ext/quaternion_common.hpp
@@ -62,7 +62,7 @@ namespace glm
 	/// @tparam T A floating-point scalar type
 	/// @tparam Q A value from qualifier enum
 	template<typename T, qualifier Q>
-	GLM_FUNC_DECL qua<T, Q> lerp(qua<T, Q> const& x, qua<T, Q> const& y, T a);
+	GLM_FUNC_DECL GLM_CONSTEXPR qua<T, Q> lerp(qua<T, Q> const& x, qua<T, Q> const& y, T a);
 
 	/// Spherical linear interpolation of two quaternions.
 	/// The interpolation always take the short path and the rotation is performed at constant speed.
diff --git a/glm/ext/quaternion_common.inl b/glm/ext/quaternion_common.inl
index 4b4d0f80..d19df8b4 100644
--- a/glm/ext/quaternion_common.inl
+++ b/glm/ext/quaternion_common.inl
@@ -26,7 +26,7 @@ namespace glm
 	}
 
 	template<typename T, qualifier Q>
-	GLM_FUNC_QUALIFIER qua<T, Q> lerp(qua<T, Q> const& x, qua<T, Q> const& y, T a)
+	GLM_FUNC_QUALIFIER GLM_CONSTEXPR qua<T, Q> lerp(qua<T, Q> const& x, qua<T, Q> const& y, T a)
 	{
 		GLM_STATIC_ASSERT(std::numeric_limits<T>::is_iec559, "'lerp' only accept floating-point inputs");