--- pp.c.0	2012-01-06 01:07:34.511988700 +0100
+++ pp.c	2012-01-06 19:04:06.311428300 +0100
@@ -515,9 +515,11 @@
 	SvTEMP_off(sv);
 	SvREFCNT_inc_void_NN(sv);
     }
-    else if (SvPADTMP(sv) && !IS_PADGV(sv))
+    else if (SvPADTMP(sv) && !IS_PADGV(sv)) {
+        Perl_ck_warner(aTHX_ packWARN(WARN_MISC),
+	     "Implicit copy of a read-only scalar due to aliasing");
         sv = newSVsv(sv);
-    else {
+    } else {
 	SvTEMP_off(sv);
 	SvREFCNT_inc_void_NN(sv);
     }