Index: gcc/testsuite/g++.dg/pr54442.C
===================================================================
--- gcc/testsuite/g++.dg/pr54442.C	(revision 0)
+++ gcc/testsuite/g++.dg/pr54442.C	(working copy)
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+
+struct S
+{
+  void s (int) const throw ();
+  void s (int) throw ();
+};
+
+typedef int index_t;
+
+void (S::*f) (index_t)       = &S::s;
+void (S::*g) (index_t) const = &S::s;
Index: gcc/tree.c
===================================================================
--- gcc/tree.c	(revision 211374)
+++ gcc/tree.c	(working copy)
@@ -6319,22 +6319,25 @@ build_qualified_type (tree type, int typ
 		TYPE_ALIGN (t) = TYPE_ALIGN (atomic_type);
 	    }
 	}
 
       if (TYPE_STRUCTURAL_EQUALITY_P (type))
 	/* Propagate structural equality. */
 	SET_TYPE_STRUCTURAL_EQUALITY (t);
       else if (TYPE_CANONICAL (type) != type)
 	/* Build the underlying canonical type, since it is different
 	   from TYPE. */
-	TYPE_CANONICAL (t) = build_qualified_type (TYPE_CANONICAL (type),
-						   type_quals);
+	{
+	  tree c = build_qualified_type (TYPE_CANONICAL (type),
+					 type_quals);
+	  TYPE_CANONICAL (t) = TYPE_CANONICAL (c);
+	}
       else
 	/* T is its own canonical type. */
 	TYPE_CANONICAL (t) = t;
 
     }
 
   return t;
 }
 
 /* Create a variant of type T with alignment ALIGN.  */