diff --git a/Doc/c-api/tuple.rst b/Doc/c-api/tuple.rst
index 25df397..62bc9a5 100644
--- a/Doc/c-api/tuple.rst
+++ b/Doc/c-api/tuple.rst
@@ -182,10 +182,13 @@
    +-----------+------------------+-----------------------------------------+
 
 
-.. c:var:: char* PyStructSequence_UnnamedField
+.. c:var:: const char * const PyStructSequence_UnnamedField
 
    Special value for a field name to leave it unnamed.
 
+   .. versionchanged:: 3.9
+      The type was changed from ``char *``.
+
 
 .. c:function:: PyObject* PyStructSequence_New(PyTypeObject *type)
 
diff --git a/Doc/whatsnew/3.9.rst b/Doc/whatsnew/3.9.rst
index b1beb0b..6e9ddc5 100644
--- a/Doc/whatsnew/3.9.rst
+++ b/Doc/whatsnew/3.9.rst
@@ -215,6 +215,9 @@
   way to call a callable Python object without any argument.
   (Contributed by Victor Stinner in :issue:`37194`.)
 
+* The global variable :c:data:`PyStructSequence_UnnamedField` is now a constant
+  and refers to a constant string.
+  (Contributed by Serhiy Storchaka in :issue:`38650`.)
 
 
 Deprecated
diff --git a/Include/structseq.h b/Include/structseq.h
index e5e5d5c..8f51c89 100644
--- a/Include/structseq.h
+++ b/Include/structseq.h
@@ -19,7 +19,7 @@
     int n_in_sequence;
 } PyStructSequence_Desc;
 
-extern char* PyStructSequence_UnnamedField;
+extern const char * const PyStructSequence_UnnamedField;
 
 #ifndef Py_LIMITED_API
 PyAPI_FUNC(void) PyStructSequence_InitType(PyTypeObject *type,
diff --git a/Misc/NEWS.d/next/C API/2019-10-30-22-03-03.bpo-38650.0pi8zt.rst b/Misc/NEWS.d/next/C API/2019-10-30-22-03-03.bpo-38650.0pi8zt.rst
new file mode 100644
index 0000000..55b9c13
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2019-10-30-22-03-03.bpo-38650.0pi8zt.rst
@@ -0,0 +1,2 @@
+The global variable :c:data:`PyStructSequence_UnnamedField` is now a
+constant and refers to a constant string.
diff --git a/Objects/structseq.c b/Objects/structseq.c
index c158afc..c86fbe5 100644
--- a/Objects/structseq.c
+++ b/Objects/structseq.c
@@ -18,7 +18,7 @@
 
 /* Fields with this name have only a field index, not a field name.
    They are only allowed for indices < n_visible_fields. */
-char *PyStructSequence_UnnamedField = "unnamed field";
+const char * const PyStructSequence_UnnamedField = "unnamed field";
 _Py_IDENTIFIER(n_sequence_fields);
 _Py_IDENTIFIER(n_fields);
 _Py_IDENTIFIER(n_unnamed_fields);