diff --git a/stubs/protobuf/METADATA.toml b/stubs/protobuf/METADATA.toml
index 06628e4dc..ad087c2d7 100644
--- a/stubs/protobuf/METADATA.toml
+++ b/stubs/protobuf/METADATA.toml
@@ -1,2 +1,2 @@
-version = "3.20.*"
+version = "4.21.*"
 extra_description = "Generated with aid from mypy-protobuf v3.4.0"
diff --git a/stubs/protobuf/google/__init__.pyi b/stubs/protobuf/google/__init__.pyi
deleted file mode 100644
index e69de29bb..000000000
diff --git a/tests/mypy_test.py b/tests/mypy_test.py
index b0da93eec..a0069ae69 100644
--- a/tests/mypy_test.py
+++ b/tests/mypy_test.py
@@ -32,6 +32,12 @@ from utils import (
     strip_comments,
 )
 
+try:
+    from mypy.api import run as mypy_run
+except ImportError:
+    print_error("Cannot import mypy. Did you install it?")
+    sys.exit(1)
+
 SUPPORTED_VERSIONS = ["3.11", "3.10", "3.9", "3.8", "3.7"]
 SUPPORTED_PLATFORMS = ("linux", "win32", "darwin")
 DIRECTORIES_TO_TEST = [Path("stdlib"), Path("stubs")]
@@ -198,13 +204,7 @@ def add_configuration(configurations: list[MypyDistConf], distribution: str) ->
         configurations.append(MypyDistConf(module_name, values.copy()))
 
 
-def run_mypy(args: TestConfig, configurations: list[MypyDistConf], files: list[Path]) -> ReturnCode:
-    try:
-        from mypy.api import run as mypy_run
-    except ImportError:
-        print_error("Cannot import mypy. Did you install it?")
-        sys.exit(1)
-
+def run_mypy(args: TestConfig, configurations: list[MypyDistConf], files: list[Path], *, testing_stdlib: bool) -> ReturnCode:
     with tempfile.NamedTemporaryFile("w+") as temp:
         temp.write("[mypy]\n")
         for dist_conf in configurations:
@@ -213,7 +213,7 @@ def run_mypy(args: TestConfig, configurations: list[MypyDistConf], files: list[P
                 temp.write(f"{k} = {v}\n")
         temp.flush()
 
-        flags = get_mypy_flags(args, temp.name)
+        flags = get_mypy_flags(args, temp.name, testing_stdlib=testing_stdlib)
         mypy_args = [*flags, *map(str, files)]
         if args.verbose:
             print("running mypy", " ".join(mypy_args))
@@ -238,8 +238,8 @@ def run_mypy(args: TestConfig, configurations: list[MypyDistConf], files: list[P
         return exit_code
 
 
-def get_mypy_flags(args: TestConfig, temp_name: str) -> list[str]:
-    return [
+def get_mypy_flags(args: TestConfig, temp_name: str, *, testing_stdlib: bool) -> list[str]:
+    flags = [
         "--python-version",
         args.version,
         "--show-traceback",
@@ -260,6 +260,9 @@ def get_mypy_flags(args: TestConfig, temp_name: str) -> list[str]:
         "--config-file",
         temp_name,
     ]
+    if not testing_stdlib:
+        flags.append("--explicit-package-bases")
+    return flags
 
 
 def add_third_party_files(
@@ -315,7 +318,14 @@ def test_third_party_distribution(distribution: str, args: TestConfig) -> TestRe
         print_error("no files found")
         sys.exit(1)
 
-    code = run_mypy(args, configurations, files)
+    prev_mypypath = os.getenv("MYPYPATH")
+    os.environ["MYPYPATH"] = os.pathsep.join(str(Path("stubs", dist)) for dist in seen_dists)
+    code = run_mypy(args, configurations, files, testing_stdlib=False)
+    if prev_mypypath is None:
+        del os.environ["MYPYPATH"]
+    else:
+        os.environ["MYPYPATH"] = prev_mypypath
+
     return TestResults(code, len(files))
 
 
@@ -333,8 +343,8 @@ def test_stdlib(code: int, args: TestConfig) -> TestResults:
 
     if files:
         print(f"Testing stdlib ({len(files)} files)...")
-        print("Running mypy " + " ".join(get_mypy_flags(args, "/tmp/...")))
-        this_code = run_mypy(args, [], files)
+        print("Running mypy " + " ".join(get_mypy_flags(args, "/tmp/...", testing_stdlib=True)))
+        this_code = run_mypy(args, [], files, testing_stdlib=True)
         code = max(code, this_code)
 
     return TestResults(code, len(files))
@@ -342,7 +352,7 @@ def test_stdlib(code: int, args: TestConfig) -> TestResults:
 
 def test_third_party_stubs(code: int, args: TestConfig) -> TestResults:
     print("Testing third-party packages...")
-    print("Running mypy " + " ".join(get_mypy_flags(args, "/tmp/...")))
+    print("Running mypy " + " ".join(get_mypy_flags(args, "/tmp/...", testing_stdlib=False)))
     files_checked = 0
     gitignore_spec = get_gitignore_spec()