diff --git a/panda/src/pipeline/pythonThread.cxx b/panda/src/pipeline/pythonThread.cxx
index 12b7d4eadf..b9b7e4ba5a 100644
--- a/panda/src/pipeline/pythonThread.cxx
+++ b/panda/src/pipeline/pythonThread.cxx
@@ -54,9 +54,11 @@ PythonThread(PyObject *function, PyObject *args,
     }
   }
 
+#ifndef SIMPLE_THREADS
   // Ensure that the Python threading system is initialized and ready
   // to go.
   PyEval_InitThreads();
+#endif
 }
 
 ////////////////////////////////////////////////////////////////////
@@ -102,9 +104,16 @@ join() {
 void PythonThread::
 thread_main() {
   // Create a new Python thread state data structure, so Python can
-  // properly lock itself.
-  PyGILState_STATE gstate;
-  gstate = PyGILState_Ensure();
+  // properly lock itself.  We can't use the PyGILState interface,
+  // which assumes we are using true OS-level threading (and we might
+  // be just using SIMPLE_THREADS).  PyGILState enforces policies like
+  // only one thread state per OS-level thread, which is not true in
+  // the case of SIMPLE_THREADS.
+
+  PyThreadState *orig_thread_state = PyThreadState_Get();
+  PyInterpreterState *istate = orig_thread_state->interp;
+  PyThreadState *new_thread_state = PyThreadState_New(istate);
+  PyThreadState_Swap(new_thread_state);
 
   // Call the user's function.
   _result = PyObject_Call(_function, _args, NULL);
@@ -112,8 +121,9 @@ thread_main() {
     handle_python_exception();
   }
 
-  // Release the thread state data structure.
-  PyGILState_Release(gstate);
+  PyThreadState_Swap(orig_thread_state);
+  PyThreadState_Clear(new_thread_state);
+  PyThreadState_Delete(new_thread_state);
 }
 
 ////////////////////////////////////////////////////////////////////