diff --git a/nsprpub/pr/include/private/primpl.h b/nsprpub/pr/include/private/primpl.h
index eb1dd716e2a..328d0f1fbb0 100644
--- a/nsprpub/pr/include/private/primpl.h
+++ b/nsprpub/pr/include/private/primpl.h
@@ -1735,6 +1735,7 @@ extern void _PR_InitMW(void);
 extern void _PR_InitRWLocks(void);
 extern void _PR_NotifyCondVar(PRCondVar *cvar, PRThread *me);
 extern void _PR_CleanupThread(PRThread *thread);
+extern void _PR_CleanupStacks(void);
 extern void _PR_CleanupTPD(void);
 extern void _PR_Cleanup(void);
 extern void _PR_LogCleanup(void);
diff --git a/nsprpub/pr/src/misc/prinit.c b/nsprpub/pr/src/misc/prinit.c
index 46cd57df417..78c4dff3296 100644
--- a/nsprpub/pr/src/misc/prinit.c
+++ b/nsprpub/pr/src/misc/prinit.c
@@ -446,6 +446,7 @@ PR_IMPLEMENT(PRStatus) PR_Cleanup()
          * Ideally, for each _PR_InitXXX(), there should be a corresponding
          * _PR_XXXCleanup() that we can call here.
          */
+        _PR_CleanupStacks();
         _PR_CleanupBeforeExit();
         _pr_initialized = PR_FALSE;
         return PR_SUCCESS;
diff --git a/nsprpub/pr/src/threads/combined/prustack.c b/nsprpub/pr/src/threads/combined/prustack.c
index aa7d2bfada0..3f12c568d01 100644
--- a/nsprpub/pr/src/threads/combined/prustack.c
+++ b/nsprpub/pr/src/threads/combined/prustack.c
@@ -58,6 +58,14 @@ void _PR_InitStacks(void)
     _pr_stackLock = PR_NewLock();
 }
 
+void _PR_CleanupStacks(void)
+{
+    if (_pr_stackLock) {
+        PR_DestroyLock(_pr_stackLock);
+        _pr_stackLock = NULL;
+    }
+}
+
 /*
 ** Allocate a stack for a thread.
 */