diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 913d007a126d72..87914ade5b518f 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -1013,8 +1013,24 @@ def four_freevars():
             three_freevars.__code__,
             three_freevars.__globals__,
             closure=my_closure)
+        my_closure = tuple(my_closure)
+
+        # should fail: anything passed to closure= isn't allowed
+        # when the source is a string
+        self.assertRaises(TypeError,
+            exec,
+            "pass",
+            closure=int)
+
+        # should fail: correct closure= argument isn't allowed
+        # when the source is a string
+        self.assertRaises(TypeError,
+            exec,
+            "pass",
+            closure=my_closure)
 
         # should fail: closure tuple with one non-cell-var
+        my_closure = list(my_closure)
         my_closure[0] = int
         my_closure = tuple(my_closure)
         self.assertRaises(TypeError,
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-02-13-05-09-31.gh-issue-130070.C8c9gK.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-02-13-05-09-31.gh-issue-130070.C8c9gK.rst
new file mode 100644
index 00000000000000..f9e135f1902b8a
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-02-13-05-09-31.gh-issue-130070.C8c9gK.rst
@@ -0,0 +1 @@
+Fixed an assertion error for :func:`exec` passed a string ``source`` and a non-``None`` ``closure``. Patch by Bartosz Sławecki.
diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 46a6fd9a8ef017..0c7b45c0b9b48d 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -1175,6 +1175,7 @@ builtin_exec_impl(PyObject *module, PyObject *source, PyObject *globals,
         if (closure != NULL) {
             PyErr_SetString(PyExc_TypeError,
                 "closure can only be used when source is a code object");
+            goto error;
         }
         PyObject *source_copy;
         const char *str;