diff --git a/Include/internal/pycore_pyatomic_ft_wrappers.h b/Include/internal/pycore_pyatomic_ft_wrappers.h
index fafdd728a8229a..d8ec306a0dae3f 100644
--- a/Include/internal/pycore_pyatomic_ft_wrappers.h
+++ b/Include/internal/pycore_pyatomic_ft_wrappers.h
@@ -138,6 +138,7 @@ extern "C" {
 #define FT_ATOMIC_ADD_SSIZE(value, new_value) \
     (void)_Py_atomic_add_ssize(&value, new_value)
 #define FT_MUTEX_LOCK(lock) PyMutex_Lock(lock)
+#define FT_MUTEX_LOCK_FLAGS(lock, flags) PyMutex_LockFlags(lock, flags)
 #define FT_MUTEX_UNLOCK(lock) PyMutex_Unlock(lock)
 
 #else
@@ -201,6 +202,7 @@ extern "C" {
 #define FT_ATOMIC_STORE_ULLONG_RELAXED(value, new_value) value = new_value
 #define FT_ATOMIC_ADD_SSIZE(value, new_value) (void)(value += new_value)
 #define FT_MUTEX_LOCK(lock) do {} while (0)
+#define FT_MUTEX_LOCK_FLAGS(lock, flags) do {} while (0)
 #define FT_MUTEX_UNLOCK(lock) do {} while (0)
 
 #endif
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-04-29-15-10-59.gh-issue-149162.BPPyrq.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-04-29-15-10-59.gh-issue-149162.BPPyrq.rst
new file mode 100644
index 00000000000000..b4c443ecee07ad
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-04-29-15-10-59.gh-issue-149162.BPPyrq.rst
@@ -0,0 +1,3 @@
+Fix a potential deadlock in :c:func:`PyUnicode_InternFromString` and other
+interning functions in the :term:`free-threaded build` when called from C++
+static local initializers.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 9aee7120c811de..892a50433f79ae 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -14347,7 +14347,7 @@ intern_common(PyInterpreterState *interp, PyObject *s /* stolen */,
     }
 #endif
 
-    FT_MUTEX_LOCK(INTERN_MUTEX);
+    FT_MUTEX_LOCK_FLAGS(INTERN_MUTEX, _Py_LOCK_DONT_DETACH);
     PyObject *t;
     {
         int res = PyDict_SetDefaultRef(interned, s, s, &t);