diff --git a/numpy/_core/src/multiarray/convert_datatype.c b/numpy/_core/src/multiarray/convert_datatype.c
index a0f09b71a3..7317d82ae5 100644
--- a/numpy/_core/src/multiarray/convert_datatype.c
+++ b/numpy/_core/src/multiarray/convert_datatype.c
@@ -63,6 +63,37 @@ static PyObject *
 PyArray_GetObjectToGenericCastingImpl(void);
 
 
+static PyObject *
+ensure_castingimpl_exists(PyArray_DTypeMeta *from, PyArray_DTypeMeta *to) {
+    if (from != to) {
+        /* A cast function must have been registered */
+        PyArray_VectorUnaryFunc *castfunc = PyArray_GetCastFunc(
+                from->singleton, to->type_num);
+        if (castfunc == NULL) {
+            PyErr_Clear();
+            /* Remember that this cast is not possible */
+            if (PyDict_SetItem(NPY_DT_SLOTS(from)->castingimpls,
+                        (PyObject *) to, Py_None) < 0) {
+                return NULL;
+            }
+            Py_RETURN_NONE;
+        }
+    }
+
+    /* PyArray_AddLegacyWrapping_CastingImpl find the correct casting level: */
+    /*
+    * TODO: Possibly move this to the cast registration time. But if we do
+    *       that, we have to also update the cast when the casting safety
+    *       is registered.
+    */
+    if (PyArray_AddLegacyWrapping_CastingImpl(from, to, -1) < 0) {
+        return NULL;
+    }
+    /* The castingimpl now always exists (or is None, so we can recurse) */
+    return PyArray_GetCastingImpl(from, to);
+}
+
+
 /**
  * Fetch the casting implementation from one DType to another.
  *
@@ -75,15 +106,14 @@ PyArray_GetObjectToGenericCastingImpl(void);
 NPY_NO_EXPORT PyObject *
 PyArray_GetCastingImpl(PyArray_DTypeMeta *from, PyArray_DTypeMeta *to)
 {
-    PyObject *res;
+    PyObject *res = NULL;
     if (from == to) {
-        res = (PyObject *)NPY_DT_SLOTS(from)->within_dtype_castingimpl;
+        res = Py_XNewRef((PyObject *)NPY_DT_SLOTS(from)->within_dtype_castingimpl);
     }
-    else {
-        res = PyDict_GetItemWithError(NPY_DT_SLOTS(from)->castingimpls, (PyObject *)to);
+    else if (PyDict_GetItemRef(NPY_DT_SLOTS(from)->castingimpls, (PyObject *)to, &res) < 0) {
+        return NULL;
     }
-    if (res != NULL || PyErr_Occurred()) {
-        Py_XINCREF(res);
+    if (res != NULL) {
         return res;
     }
     /*
@@ -120,31 +150,20 @@ PyArray_GetCastingImpl(PyArray_DTypeMeta *from, PyArray_DTypeMeta *to)
         return NULL;
     }
     else {
-        if (from != to) {
-            /* A cast function must have been registered */
-            PyArray_VectorUnaryFunc *castfunc = PyArray_GetCastFunc(
-                    from->singleton, to->type_num);
-            if (castfunc == NULL) {
-                PyErr_Clear();
-                /* Remember that this cast is not possible */
-                if (PyDict_SetItem(NPY_DT_SLOTS(from)->castingimpls,
-                            (PyObject *) to, Py_None) < 0) {
-                    return NULL;
-                }
-                Py_RETURN_NONE;
-            }
-        }
-
-        /* PyArray_AddLegacyWrapping_CastingImpl find the correct casting level: */
         /*
-         * TODO: Possibly move this to the cast registration time. But if we do
-         *       that, we have to also update the cast when the casting safety
-         *       is registered.
+         * We need to create and add the CastingImpl while making sure no other
+         * threads does so.  Before we add it check again (another thread may
+         * have added it in the meantime).
          */
-        if (PyArray_AddLegacyWrapping_CastingImpl(from, to, -1) < 0) {
-            return NULL;
+        Py_BEGIN_CRITICAL_SECTION((NPY_DT_SLOTS(from)->castingimpls));
+        if (PyDict_GetItemRef(NPY_DT_SLOTS(from)->castingimpls, (PyObject *)to, &res) < 0) {
+            /* We will return NULL on error */
         }
-        return PyArray_GetCastingImpl(from, to);
+        else if (res == NULL) {
+            res = ensure_castingimpl_exists(from, to);
+        }
+        Py_END_CRITICAL_SECTION();
+        return res;
     }
 
     if (res == NULL) {