diff --git a/include/boost/bimap/relation/mutant_relation.hpp b/include/boost/bimap/relation/mutant_relation.hpp
index 1681a9d0..6897ca26 100644
--- a/include/boost/bimap/relation/mutant_relation.hpp
+++ b/include/boost/bimap/relation/mutant_relation.hpp
@@ -289,8 +289,14 @@ class mutant_relation : public
 
     // Operators
 
-    template< bool FM >
-    mutant_relation& operator=(const mutant_relation<TA,TB,Info,FM> & rel)
+    mutant_relation& operator=(const mutant_relation & rel)
+    {
+	base_::change_to(rel);
+	return *this;
+    }
+
+    mutant_relation& operator=(const mutant_relation<TA,TB,Info,
+						     !force_mutable> & rel)
     {
         base_::change_to(rel);
         return *this;