diff --git a/Lib/test/test_interpreters/test_api.py b/Lib/test/test_interpreters/test_api.py
index a9e296891bb8705..1ceb5916bd5f9f5 100644
--- a/Lib/test/test_interpreters/test_api.py
+++ b/Lib/test/test_interpreters/test_api.py
@@ -947,6 +947,16 @@ def test_failure(self):
         with self.assertRaises(ExecutionFailed):
             interp.exec('raise Exception')
 
+    def test_failure_with_broken_exception_str(self):
+        interp = interpreters.create()
+        with self.assertRaises(interpreters.InterpreterError):
+            interp.exec(dedent("""
+                class BrokenError(Exception):
+                    def __str__(self):
+                        raise ValueError
+                raise BrokenError
+                """))
+
     @force_not_colorized
     def test_display_preserved_exception(self):
         tempdir = self.temp_dir()
diff --git a/Misc/NEWS.d/next/Library/2026-11-14-21-04-56.gh-issue-161996.35uL2d.rst b/Misc/NEWS.d/next/Library/2026-11-14-21-04-56.gh-issue-161996.35uL2d.rst
new file mode 100644
index 000000000000000..561bb62d6537073
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-11-14-21-04-56.gh-issue-161996.35uL2d.rst
@@ -0,0 +1,2 @@
+Fix a crash in :meth:`concurrent.interpreters.Interpreter.exec` when the
+uncaught exception's ``__str__`` raises.
diff --git a/Python/crossinterp.c b/Python/crossinterp.c
index d189d7bcefe313e..a91b45ba2cbcf45 100644
--- a/Python/crossinterp.c
+++ b/Python/crossinterp.c
@@ -2018,6 +2018,14 @@ _PyXI_ApplyError(_PyXI_error *error, const char *failure)
     PyThreadState *tstate = PyThreadState_Get();
 
     if (failure != NULL) {
+        if (error->override != NULL
+            && error->override->code == _PyXI_ERR_NO_MEMORY)
+        {
+            PyErr_NoMemory();
+        }
+        else {
+            PyErr_SetString(PyExc_InterpreterError, failure);
+        }
         xi_error_clear(error);
         return NULL;
     }