diff --git a/pyproject.toml b/pyproject.toml
index f854d47bc6..b6c4891bc9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -38,6 +38,10 @@ show_error_codes = true
 # Warn of unreachable or redundant code.
 warn_unreachable = true
 
+# dmypy enables local_partial_types implicitly. We need mypy to align
+# with this behavior.
+local_partial_types = true
+
 [[tool.mypy.overrides]]
 module = ["zproject.configured_settings", "zproject.settings"]
 no_implicit_reexport = false
diff --git a/tools/run-dev.py b/tools/run-dev.py
index 045b94b124..aac1f4a392 100755
--- a/tools/run-dev.py
+++ b/tools/run-dev.py
@@ -338,7 +338,7 @@ def print_listeners() -> None:
     print()
 
 
-children = []
+children: List["subprocess.Popen[bytes]"] = []
 
 
 async def serve() -> None: