diff --git a/include/pybind11/gil.h b/include/pybind11/gil.h
index 570a5581..eb72e15e 100644
--- a/include/pybind11/gil.h
+++ b/include/pybind11/gil.h
@@ -138,6 +138,7 @@ class gil_scoped_acquire {
 class gil_scoped_release {
 public:
     explicit gil_scoped_release(bool disassoc = false) : disassoc(disassoc) {
+        assert(PyGILState_Check());
         // `get_internals()` must be called here unconditionally in order to initialize
         // `internals.tstate` for subsequent `gil_scoped_acquire` calls. Otherwise, an
         // initialization race could occur as multiple threads try `gil_scoped_acquire`.