diff --git a/Include/pystate.h b/Include/pystate.h
--- a/Include/pystate.h
+++ b/Include/pystate.h
@@ -212,6 +212,11 @@
 */
 PyAPI_FUNC(PyThreadState *) PyGILState_GetThisThreadState(void);
 
+/* Helper/diagnostic function - return 1 if the current thread
+ * currently holds the GIL, 0 otherwise
+ */
+PyAPI_FUNC(int) PyGILState_Check(void);
+
 #endif   /* #ifdef WITH_THREAD */
 
 /* The implementation of sys._current_frames()  Returns a dict mapping
diff --git a/Python/pystate.c b/Python/pystate.c
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -697,6 +697,15 @@
     return (PyThreadState *)PyThread_get_key_value(autoTLSkey);
 }
 
+int
+PyGILState_Check(void)
+{
+    /* can't use PyThreadState_Get() since it will assert that it has the GIL */
+    PyThreadState *tstate = (PyThreadState*)_Py_atomic_load_relaxed(
+        &_PyThreadState_Current);
+    return tstate && (tstate == PyGILState_GetThisThreadState());
+}
+
 PyGILState_STATE
 PyGILState_Ensure(void)
 {