diff --git a/Lib/tkinter/test/test_tkinter/test_misc.py b/Lib/tkinter/test/test_tkinter/test_misc.py
@@ -1,10 +1,22 @@
 import unittest
+import subprocess
+import sys
+import threading
 import tkinter
 from test import support
 from tkinter.test.support import AbstractTkTest
 
 support.requires('gui')
 
+def test_thread_gc():
+    root = tkinter.Tk()
+    root.destroy()
+    ev = threading.Event()
+    threading.Thread(target=lambda obj: ev.wait(), args=(root,)).start()
+    del root
+    ev.set()
+    print("passed")
+
 class MiscTest(AbstractTkTest, unittest.TestCase):
 
     def test_all(self):
@@ -26,6 +38,25 @@ def test_repr(self):
         f = tkinter.Frame(t, name='child')
         self.assertEqual(repr(f), '<tkinter.Frame object .top.child>')
 
+    def test_thread_gc(self):
+        p = subprocess.Popen([sys.executable, "-c",
+                              "from tkinter.test.test_tkinter import test_misc; "
+                              "test_misc.test_thread_gc()"],
+                             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+        stdout, stderr = p.communicate()
+        stderr = stderr.strip()
+        try:
+            self.assertTrue(b"Exception ignored in: <class 'RuntimeWarning'>" in stderr)
+            self.assertTrue(b"RuntimeWarning: Deallocation of Tkapp attempted in wrong "
+                            b"thread. Skipping deletion of Tcl interpreter (this will "
+                            b"cause a memory leak)." in stderr)
+        except AssertionError:
+            # If there is an error in the subprocess
+            # we need to be able to debug it
+            print(stderr.decode("utf-8"), file=sys.stderr)
+            raise
+        self.assertEqual(stdout.strip(), b"passed")
+
     def test_generated_names(self):
         t = tkinter.Toplevel(self.root)
         f = tkinter.Frame(t)

diff --git a/Misc/NEWS.d/next/Library/2020-07-18-13-44-24.bpo-39093.yhmJSn.rst b/Misc/NEWS.d/next/Library/2020-07-18-13-44-24.bpo-39093.yhmJSn.rst
@@ -0,0 +1 @@
+Fixed crash when Tcl interpreter was deallocated in wrong thread
diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
@@ -3040,10 +3040,19 @@ static void
 Tkapp_Dealloc(PyObject *self)
 {
     PyObject *tp = (PyObject *) Py_TYPE(self);
-    /*CHECK_TCL_APPARTMENT;*/
-    ENTER_TCL
-    Tcl_DeleteInterp(Tkapp_Interp(self));
-    LEAVE_TCL
+    if (((TkappObject *)self)->threaded && \
+        ((TkappObject *)self)->thread_id != Tcl_GetCurrentThread()) {
+        // We cannot delete the interpreter in the wrong thread (bpo-39093)
+        PyErr_SetString(PyExc_RuntimeWarning, "Deallocation of Tkapp " \
+            "attempted in wrong thread. Skipping deletion of Tcl " \
+            "interpreter (this will cause a memory leak).");
+        PyErr_WriteUnraisable(PyErr_Occurred());
+        PyErr_Clear();
+    } else {
+        ENTER_TCL
+        Tcl_DeleteInterp(Tkapp_Interp(self));
+        LEAVE_TCL
+    }
     PyObject_Del(self);
     Py_DECREF(tp);
     DisableEventHook();
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Fixed crash when Tcl interpreter was deallocated in wrong thread