fix lvalue context for 4-arg substr

4-arg substr uses its first arg as an lvalue, but wasn't lvaluifying
it properly.  [perl #115258]

1 files changed, 1 insertions, 1 deletions

diff --git a/op.c b/op.c
index c617ad2a00..2e4dae43c6 100644
--- a/op.c
+++ b/op.c
@@ -13385,7 +13385,7 @@ Perl_ck_substr(pTHX_ OP *o)
 	if (kid->op_type == OP_NULL)
 	    kid = OpSIBLING(kid);
 	if (kid)
-	    kid->op_flags |= OPf_MOD;
+	    op_lvalue(kid, o->op_type);
 
     }
     return o;