1 files changed, 2 insertions, 1 deletions
diff --git a/doio.c b/doio.c
index 5682426da9..fd6683da26 100644
--- a/doio.c
+++ b/doio.c
@@ -2283,9 +2283,10 @@ Perl_do_shmio(pTHX_ I32 optype, SV **mark, SV **sp)
     if (optype == OP_SHMREAD) {
 	char *mbuf;
 	/* suppress warning when reading into undef var (tchrist 3/Mar/00) */
+	SvGETMAGIC(mstr);
+	SvUPGRADE(mstr, SVt_PV);
 	if (! SvOK(mstr))
 	    sv_setpvs(mstr, "");
-	SvUPGRADE(mstr, SVt_PV);
 	SvPOK_only(mstr);
 	mbuf = SvGROW(mstr, (STRLEN)msize+1);