diff --git a/quaternion.cpp b/quaternion.cpp
index df03f42c..967a512d 100644
--- a/quaternion.cpp
+++ b/quaternion.cpp
@@ -356,17 +356,19 @@ cruft::operator<< (std::ostream &os, const quaternion<T> q)
 
 
 ///////////////////////////////////////////////////////////////////////////////
-namespace cruft::debug {
-    template <typename T>
-    struct validator<quaternion<T>> {
-        static constexpr
-        bool
-        is_valid (const quaternion<T> &q)
-        {
-            return is_normalised (q);
-        }
-    };
-}
+template <typename ValueT>
+struct cruft::debug::validator<quaternion<ValueT>> {
+    static constexpr
+    bool
+    is_valid (const quaternion<ValueT> &q)
+    {
+        return is_normalised (q);
+    }
+};
+
+
+//-----------------------------------------------------------------------------
+template struct cruft::debug::validator<::cruft::quaternion<float>>;
 
 
 ///////////////////////////////////////////////////////////////////////////////