diff --git a/py/objfun.c b/py/objfun.c
index a94978e3a4..80cee1643b 100644
--- a/py/objfun.c
+++ b/py/objfun.c
@@ -249,7 +249,7 @@ continue2:;
         mp_obj_t *d = &flat_args[self->n_args - 1];
         mp_obj_t *s = &self->extra_args[self->n_def_args - 1];
         for (int i = self->n_def_args; i > 0; i--) {
-            if (*d != MP_OBJ_NULL) {
+            if (*d == MP_OBJ_NULL) {
                 *d-- = *s--;
             }
         }
diff --git a/tests/basics/fun-defargs2.py b/tests/basics/fun-defargs2.py
new file mode 100644
index 0000000000..c9090a3cd2
--- /dev/null
+++ b/tests/basics/fun-defargs2.py
@@ -0,0 +1,13 @@
+# overriding default arguments
+
+def foo(a, b=3):
+    print(a, b)
+
+# override with positional
+foo(1, 333)
+
+# override with keyword
+foo(1, b=333)
+
+# override with keyword
+foo(a=2, b=333)