1 files changed, 12 insertions, 2 deletions
diff --git a/vm_backtrace.c b/vm_backtrace.c
index 0493ed8c89..776f6d188a 100644
--- a/vm_backtrace.c
+++ b/vm_backtrace.c
@@ -33,8 +33,18 @@ inline static int
 calc_lineno(const rb_iseq_t *iseq, const VALUE *pc)
 {
     size_t pos = (size_t)(pc - iseq->body->iseq_encoded);
-    /* use pos-1 because PC points next instruction at the beginning of instruction */
-    return rb_iseq_line_no(iseq, pos - 1);
+    if (LIKELY(pos)) {
+        /* use pos-1 because PC points next instruction at the beginning of instruction */
+        pos--;
+    }
+#if VMDEBUG && defined(HAVE_BUILTIN___BUILTIN_TRAP)
+    else {
+        /* SDR() is not possible; that causes infinite loop. */
+        rb_print_backtrace();
+        __builtin_trap();
+    }
+#endif
+    return rb_iseq_line_no(iseq, pos);
 }
 
 int