1 files changed, 15 insertions, 1 deletions
diff --git a/Python/optimizer_cases.c.h b/Python/optimizer_cases.c.h
index deb912662e4..5d469765203 100644
--- a/Python/optimizer_cases.c.h
+++ b/Python/optimizer_cases.c.h
@@ -2124,8 +2124,22 @@
         }
 
         case _CALL_ISINSTANCE: {
+            JitOptSymbol *cls;
+            JitOptSymbol *instance;
             JitOptSymbol *res;
-            res = sym_new_not_null(ctx);
+            cls = stack_pointer[-1];
+            instance = stack_pointer[-2];
+            res = sym_new_type(ctx, &PyBool_Type);
+            PyTypeObject *inst_type = sym_get_type(instance);
+            PyTypeObject *cls_o = (PyTypeObject *)sym_get_const(ctx, cls);
+            if (inst_type && cls_o && sym_matches_type(cls, &PyType_Type)) {
+                if (inst_type == cls_o || PyType_IsSubtype(inst_type, cls_o)) {
+                    sym_set_const(res, Py_True);
+                }
+                else {
+                    sym_set_const(res, Py_False);
+                }
+            }
             stack_pointer[-4] = res;
             stack_pointer += -3;
             assert(WITHIN_STACK_BOUNDS());