diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 18b9458..276547c 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -12309,31 +12309,22 @@
     Py_RETURN_TRUE;
 }
 
-int
-PyUnicode_IsIdentifier(PyObject *self)
+Py_ssize_t
+_PyUnicode_ScanIdentifier(PyObject *self)
 {
     Py_ssize_t i;
-    int ready = PyUnicode_IS_READY(self);
+    if (PyUnicode_READY(self) == -1)
+        return -1;
 
-    Py_ssize_t len = ready ? PyUnicode_GET_LENGTH(self) : PyUnicode_GET_SIZE(self);
+    Py_ssize_t len = PyUnicode_GET_LENGTH(self);
     if (len == 0) {
         /* an empty string is not a valid identifier */
         return 0;
     }
 
-    int kind = 0;
-    const void *data = NULL;
-    const wchar_t *wstr = NULL;
-    Py_UCS4 ch;
-    if (ready) {
-        kind = PyUnicode_KIND(self);
-        data = PyUnicode_DATA(self);
-        ch = PyUnicode_READ(kind, data, 0);
-    }
-    else {
-        wstr = _PyUnicode_WSTR(self);
-        ch = wstr[0];
-    }
+    int kind = PyUnicode_KIND(self);
+    const void *data = PyUnicode_DATA(self);
+    Py_UCS4 ch = PyUnicode_READ(kind, data, 0);
     /* PEP 3131 says that the first character must be in
        XID_Start and subsequent characters in XID_Continue,
        and for the ASCII range, the 2.x rules apply (i.e
@@ -12347,17 +12338,44 @@
     }
 
     for (i = 1; i < len; i++) {
-        if (ready) {
-            ch = PyUnicode_READ(kind, data, i);
-        }
-        else {
-            ch = wstr[i];
-        }
+        ch = PyUnicode_READ(kind, data, i);
         if (!_PyUnicode_IsXidContinue(ch)) {
-            return 0;
+            return i;
         }
     }
-    return 1;
+    return i;
+}
+
+int
+PyUnicode_IsIdentifier(PyObject *self)
+{
+    if (PyUnicode_IS_READY(self)) {
+        Py_ssize_t i = _PyUnicode_ScanIdentifier(self);
+        Py_ssize_t len = PyUnicode_GET_LENGTH(self);
+        /* an empty string is not a valid identifier */
+        return len && i == len;
+    }
+    else {
+        Py_ssize_t i, len = PyUnicode_GET_SIZE(self);
+        if (len == 0) {
+            /* an empty string is not a valid identifier */
+            return 0;
+        }
+
+        const wchar_t *wstr = _PyUnicode_WSTR(self);
+        Py_UCS4 ch = wstr[0];
+        if (!_PyUnicode_IsXidStart(ch) && ch != 0x5F /* LOW LINE */) {
+            return 0;
+        }
+
+        for (i = 1; i < len; i++) {
+            ch = wstr[i];
+            if (!_PyUnicode_IsXidContinue(ch)) {
+                return 0;
+            }
+        }
+        return 1;
+    }
 }
 
 /*[clinic input]