diff --git a/peep.c b/peep.c
index 68da56f3bf13..e9de45eb0a68 100644
--- a/peep.c
+++ b/peep.c
@@ -3988,7 +3988,7 @@ Perl_rpeep(pTHX_ OP *o)
                     */
                     OP *left = OpSIBLING(right);
                     if (left->op_type == OP_SUBSTR
-                         && (left->op_private & 7) < 4) {
+                         && (cMAXARG3x(left) < 4)) {
                         op_null(o);
                         /* cut out right */
                         op_sibling_splice(o, NULL, 1, NULL);
diff --git a/pp.c b/pp.c
index cd4550c0d768..43513c3a7a53 100644
--- a/pp.c
+++ b/pp.c
@@ -3575,7 +3575,7 @@ Perl_translate_substr_offsets( STRLEN curlen, IV pos1_iv,
 }
 
 PP_wrapped(pp_substr,
-                (PL_op->op_private & 7)
+                MAXARG3
               + ((PL_op->op_private & OPpSUBSTR_REPL_FIRST) ? 1 : 0),
             0)
 {
@@ -3595,7 +3595,7 @@ PP_wrapped(pp_substr,
     SV *repl_sv = NULL;
     const char *repl = NULL;
     STRLEN repl_len;
-    int num_args = PL_op->op_private & 7;
+    int num_args = MAXARG3;
     bool repl_need_utf8_upgrade = FALSE;
 
     if (num_args > 2) {