diff --git a/mypy/dmypy_server.py b/mypy/dmypy_server.py
index 5b0e03282a4a..614b757c774d 100644
--- a/mypy/dmypy_server.py
+++ b/mypy/dmypy_server.py
@@ -151,6 +151,8 @@ def process_start_options(flags: list[str], allow_sources: bool) -> Options:
         sys.exit("dmypy: start/restart should not disable incremental mode")
     if options.follow_imports not in ("skip", "error", "normal"):
         sys.exit("dmypy: follow-imports=silent not supported")
+    if not options.local_partial_types:
+        sys.exit("dmypy: disabling local-partial-types not supported")
     return options
 
 
diff --git a/mypy/main.py b/mypy/main.py
index f4d6b18e58b6..8fecb720cc78 100644
--- a/mypy/main.py
+++ b/mypy/main.py
@@ -1254,7 +1254,13 @@ def add_invertible_flag(
     parser.add_argument("--test-env", action="store_true", help=argparse.SUPPRESS)
     # --local-partial-types disallows partial types spanning module top level and a function
     # (implicitly defined in fine-grained incremental mode)
-    add_invertible_flag("--local-partial-types", default=False, help=argparse.SUPPRESS)
+    add_invertible_flag(
+        "--no-local-partial-types",
+        inverse="--local-partial-types",
+        default=True,
+        dest="local_partial_types",
+        help=argparse.SUPPRESS,
+    )
     # --native-parser enables the native parser (experimental)
     add_invertible_flag("--native-parser", default=False, help=argparse.SUPPRESS)
     # --logical-deps adds some more dependencies that are not semantically needed, but
diff --git a/mypy/options.py b/mypy/options.py
index 79ca75c58be6..77a3e4fd0584 100644
--- a/mypy/options.py
+++ b/mypy/options.py
@@ -380,7 +380,7 @@ def __init__(self) -> None:
         self.dump_deps = False
         self.logical_deps = False
         # If True, partial types can't span a module top level and a function
-        self.local_partial_types = False
+        self.local_partial_types = True
         # If True, use the native parser (experimental)
         self.native_parser = False
         # Some behaviors are changed when using Bazel (https://bazel.build).
diff --git a/mypyc/test-data/run-classes.test b/mypyc/test-data/run-classes.test
index 877c40699cda..b3526b0dc7fb 100644
--- a/mypyc/test-data/run-classes.test
+++ b/mypyc/test-data/run-classes.test
@@ -4363,7 +4363,7 @@ from __future__ import annotations
 
 from mypy_extensions import mypyc_attr
 
-a = []
+a: list[int] = []
 
 @mypyc_attr(free_list_len=1)
 class Foo:
diff --git a/mypyc/test-data/run-tuples.test b/mypyc/test-data/run-tuples.test
index e2e8358bb43e..b410d8e4ba38 100644
--- a/mypyc/test-data/run-tuples.test
+++ b/mypyc/test-data/run-tuples.test
@@ -339,7 +339,7 @@ def test_final_tuple_not_in() -> None:
 
     assert 'x' not in TUP0
 
-log = []
+log: list[str] = []
 
 def f_a() -> str:
     log.append('f_a')
diff --git a/test-data/unit/check-custom-plugin.test b/test-data/unit/check-custom-plugin.test
index 7b1a2c2a91d7..dd1de1265b59 100644
--- a/test-data/unit/check-custom-plugin.test
+++ b/test-data/unit/check-custom-plugin.test
@@ -996,7 +996,7 @@ class M(type):
     attr = 'test'
 
 class B:
-    attr = None
+    attr = b'bytes'
 
 class Cls(B, metaclass=M):
     pass
diff --git a/test-data/unit/check-functions.test b/test-data/unit/check-functions.test
index 80a40d3ef179..a0e31fa23ce4 100644
--- a/test-data/unit/check-functions.test
+++ b/test-data/unit/check-functions.test
@@ -2622,7 +2622,7 @@ reveal_type(bar(None))  # N: Revealed type is "None"
 [out]
 
 [case testNoComplainInferredNone]
-# flags: --no-strict-optional
+# flags: --no-strict-optional --no-local-partial-types
 from typing import TypeVar, Optional
 T = TypeVar('T')
 def X(val: T) -> T: ...
@@ -2635,7 +2635,7 @@ xx: Optional[int] = X(x_in)
 from typing import TypeVar, Optional
 T = TypeVar('T')
 def X(val: T) -> T: ...
-x_in = None
+x_in = X(None)
 def Y(x: Optional[str] = X(x_in)): ...
 
 xx: Optional[int] = X(x_in)
diff --git a/test-data/unit/check-redefine2.test b/test-data/unit/check-redefine2.test
index b1a30784b99c..d8a7ccbfc4a4 100644
--- a/test-data/unit/check-redefine2.test
+++ b/test-data/unit/check-redefine2.test
@@ -1112,7 +1112,7 @@ if int():
     x = ""
 
 [file b.py]
-# mypy: allow-redefinition-new
+# mypy: local-partial-types=false, allow-redefinition-new
 x = 0
 if int():
     x = ""