diff --git a/Lib/test/test_hashlib.py b/Lib/test/test_hashlib.py
index 5c38813f3..47e2079fe 100644
--- a/Lib/test/test_hashlib.py
+++ b/Lib/test/test_hashlib.py
@@ -127,8 +127,11 @@ class HashLibTestCase(unittest.TestCase):
             algorithms.add(algorithm.lower())
 
         _blake2 = self._conditional_import_module('_blake2')
+        blake2_hashes = {'blake2b', 'blake2s'}
         if _blake2:
-            algorithms.update({'blake2b', 'blake2s'})
+            algorithms.update(blake2_hashes)
+        else:
+            algorithms.difference_update(blake2_hashes)
 
         self.constructors_to_test = {}
         for algorithm in algorithms:
@@ -220,7 +223,12 @@ class HashLibTestCase(unittest.TestCase):
         # all available algorithms must be loadable, bpo-47101
         self.assertNotIn("undefined", hashlib.algorithms_available)
         for name in hashlib.algorithms_available:
-            digest = hashlib.new(name, usedforsecurity=False)
+            with self.subTest(name):
+                try:
+                    _ = hashlib.new(name, usedforsecurity=False)
+                except ValueError as exc:
+                    self.skip_if_blake2_not_builtin(name, exc)
+                    raise
 
     def test_usedforsecurity_true(self):
         hashlib.new("sha256", usedforsecurity=True)
@@ -444,6 +452,7 @@ class HashLibTestCase(unittest.TestCase):
         self.assertEqual(h.hexdigest(), "e2d4535e3b613135c14f2fe4e026d7ad8d569db44901740beffa30d430acb038")
 
     @requires_resource('cpu')
+    @requires_blake2
     def test_blake2_update_over_4gb(self):
         # blake2s or blake2b doesn't matter based on how our C code is structured, this tests the
         # common loop macro logic.
@@ -734,6 +743,12 @@ class HashLibTestCase(unittest.TestCase):
           "e718483d0ce769644e2e42c7bc15b4638e1f98b13b2044285632a803afa973eb"+
           "de0ff244877ea60a4cb0432ce577c31beb009c5c2c49aa2e4eadb217ad8cc09b")
 
+    def skip_if_blake2_not_builtin(self, name, skip_reason):
+        # blake2 builtins may be absent if python built with
+        # a subset of --with-builtin-hashlib-hashes or none.
+        if "blake2" in name and "blake2" not in builtin_hashes:
+            self.skipTest(skip_reason)
+
     def check_blake2(self, constructor, salt_size, person_size, key_size,
                      digest_size, max_offset):
         self.assertEqual(constructor.SALT_SIZE, salt_size)
diff --git a/crates/stdlib/src/blake2.rs b/crates/stdlib/src/blake2.rs
index 53687c702..382aec826 100644
--- a/crates/stdlib/src/blake2.rs
+++ b/crates/stdlib/src/blake2.rs
@@ -7,6 +7,33 @@ mod _blake2 {
     use crate::hashlib::_hashlib::{BlakeHashArgs, local_blake2b, local_blake2s};
     use crate::vm::{PyPayload, PyResult, VirtualMachine};
 
+    #[pyattr(name = "_GIL_MINSIZE")]
+    const GIL_MINSIZE: u16 = 2048;
+
+    #[pyattr]
+    const BLAKE2B_SALT_SIZE: u8 = 16;
+
+    #[pyattr]
+    const BLAKE2B_PERSON_SIZE: u8 = 16;
+
+    #[pyattr]
+    const BLAKE2B_MAX_KEY_SIZE: u8 = 64;
+
+    #[pyattr]
+    const BLAKE2B_MAX_DIGEST_SIZE: u8 = 64;
+
+    #[pyattr]
+    const BLAKE2S_SALT_SIZE: u8 = 8;
+
+    #[pyattr]
+    const BLAKE2S_PERSON_SIZE: u8 = 8;
+
+    #[pyattr]
+    const BLAKE2S_MAX_KEY_SIZE: u8 = 32;
+
+    #[pyattr]
+    const BLAKE2S_MAX_DIGEST_SIZE: u8 = 32;
+
     #[pyfunction]
     fn blake2b(args: BlakeHashArgs, vm: &VirtualMachine) -> PyResult {
         Ok(local_blake2b(args, vm)?.into_pyobject(vm))