Make scalar assignment to undef a compile time error

2 files changed, 4 insertions, 2 deletions

diff --git a/op.c b/op.c
index 594d4ee9c3..61f7eaad75 100644
--- a/op.c
+++ b/op.c
@@ -4291,6 +4291,8 @@ Perl_op_lvalue_flags(pTHX_ OP *o, I32 type, U32 flags)
 
     switch (o->op_type) {
     case OP_UNDEF:
+        if (type == OP_SASSIGN)
+            goto nomod;
 	PL_modcount++;
 	goto do_next;
 
diff --git a/t/run/fresh_perl.t b/t/run/fresh_perl.t
index 5f0e2ce216..88a64ad583 100644
--- a/t/run/fresh_perl.t
+++ b/t/run/fresh_perl.t
@@ -194,8 +194,8 @@ BEGIN failed--compilation aborted at - line 1.
 ########
 BEGIN { undef = 0 }
 EXPECT
-Modification of a read-only value attempted at - line 1.
-BEGIN failed--compilation aborted at - line 1.
+Can't modify undef operator in scalar assignment at - line 1, near "0 }"
+BEGIN not safe after errors--compilation aborted at - line 1.
 ########
 {
     package foo;