diff --git a/Python/pystate.c b/Python/pystate.c
index 436f874..81bcf68 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -538,24 +538,25 @@ _PyInterpreterState_IDInitref(PyInterpreterState *interp)
 }
 
 
-void
+int
 _PyInterpreterState_IDIncref(PyInterpreterState *interp)
 {
-    if (interp->id_mutex == NULL) {
-        return;
+    if (_PyInterpreterState_IDInitref(interp) < 0) {
+        return -1;
     }
+
     PyThread_acquire_lock(interp->id_mutex, WAIT_LOCK);
     interp->id_refcount += 1;
     PyThread_release_lock(interp->id_mutex);
+    return 0;
 }
 
 
 void
 _PyInterpreterState_IDDecref(PyInterpreterState *interp)
 {
-    if (interp->id_mutex == NULL) {
-        return;
-    }
+    assert(interp->id_mutex != NULL);
+
     struct _gilstate_runtime_state *gilstate = &_PyRuntime.gilstate;
     PyThread_acquire_lock(interp->id_mutex, WAIT_LOCK);
     assert(interp->id_refcount != 0);