diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-03-18-10-56-53.bpo-36333.4dqemZ.rst b/Misc/NEWS.d/next/Core and Builtins/2019-03-18-10-56-53.bpo-36333.4dqemZ.rst
new file mode 100644
index 00000000000..e5af44fda40
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-03-18-10-56-53.bpo-36333.4dqemZ.rst	
@@ -0,0 +1 @@
+Fix leak in _PyRuntimeState_Fini. Contributed by Stéphane Wirtel.
diff --git a/Python/pystate.c b/Python/pystate.c
index 6a2dc102ecf..36566b76715 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -92,6 +92,11 @@ _PyRuntimeState_Fini(_PyRuntimeState *runtime)
         runtime->interpreters.mutex = NULL;
     }
 
+    if (runtime->xidregistry.mutex != NULL) {
+        PyThread_free_lock(runtime->xidregistry.mutex);
+        runtime->xidregistry.mutex = NULL;
+    }
+
     PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 }