diff --git a/Modules/md5module.c b/Modules/md5module.c
index b2e65a0..2ae94a4 100644
--- a/Modules/md5module.c
+++ b/Modules/md5module.c
@@ -484,7 +484,7 @@ static PyType_Slot md5_type_slots[] = {
 static PyType_Spec md5_type_spec = {
     .name = "_md5.md5",
     .basicsize =  sizeof(MD5object),
-    .flags = Py_TPFLAGS_DEFAULT,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
     .slots = md5_type_slots
 };
 
diff --git a/Modules/sha1module.c b/Modules/sha1module.c
index 7126db9..9ac46c5 100644
--- a/Modules/sha1module.c
+++ b/Modules/sha1module.c
@@ -462,7 +462,7 @@ static PyType_Slot sha1_type_slots[] = {
 static PyType_Spec sha1_type_spec = {
     .name = "_sha1.sha1",
     .basicsize =  sizeof(SHA1object),
-    .flags = Py_TPFLAGS_DEFAULT,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
     .slots = sha1_type_slots
 };
 
@@ -554,7 +554,7 @@ _sha1_exec(PyObject *module)
     }
 
     Py_INCREF(st->sha1_type);
-    if (PyModule_AddObject(module, 
+    if (PyModule_AddObject(module,
                            "SHA1Type",
                            (PyObject *)st->sha1_type) < 0) {
         Py_DECREF(st->sha1_type);
diff --git a/Modules/sha256module.c b/Modules/sha256module.c
index b90e5df..ccb1862 100644
--- a/Modules/sha256module.c
+++ b/Modules/sha256module.c
@@ -544,14 +544,14 @@ static PyType_Slot sha256_types_slots[] = {
 static PyType_Spec sha224_type_spec = {
     .name = "_sha256.sha224",
     .basicsize = sizeof(SHAobject),
-    .flags = Py_TPFLAGS_DEFAULT,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
     .slots = sha256_types_slots
 };
 
 static PyType_Spec sha256_type_spec = {
     .name = "_sha256.sha256",
     .basicsize = sizeof(SHAobject),
-    .flags = Py_TPFLAGS_DEFAULT,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
     .slots = sha256_types_slots
 };
 
diff --git a/Modules/sha512module.c b/Modules/sha512module.c
index 0d8f51e..5e8572c 100644
--- a/Modules/sha512module.c
+++ b/Modules/sha512module.c
@@ -602,7 +602,7 @@ static PyType_Slot sha512_sha384_type_slots[] = {
 static PyType_Spec sha512_sha384_type_spec = {
     .name = "_sha512.sha384",
     .basicsize =  sizeof(SHAobject),
-    .flags = Py_TPFLAGS_DEFAULT,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
     .slots = sha512_sha384_type_slots
 };
 
@@ -619,7 +619,7 @@ static PyType_Slot sha512_sha512_type_slots[] = {
 static PyType_Spec sha512_sha512_type_spec = {
     .name = "_sha512.sha512",
     .basicsize =  sizeof(SHAobject),
-    .flags = Py_TPFLAGS_DEFAULT,
+    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
     .slots = sha512_sha512_type_slots
 };