diff --git a/src/fromager/progress.py b/src/fromager/progress.py
index f0a26bf2..32c22c12 100644
--- a/src/fromager/progress.py
+++ b/src/fromager/progress.py
@@ -1,13 +1,21 @@
 import sys
 import typing
+from types import TracebackType
 
 import tqdm as _tqdm
 
 __all__ = ("progress",)
 
+# fix for runtime errors caused by inheriting classes that are generic in stubs but not runtime
+# https://mypy.readthedocs.io/en/latest/runtime_troubles.html#using-classes-that-are-generic-in-stubs-but-not-at-runtime
+if typing.TYPE_CHECKING:
+    ProgressBarTqdm = _tqdm.tqdm[int] | _tqdm.tqdm[typing.Never] | None
+else:
+    ProgressBarTqdm = _tqdm.tqdm | None
+
 
 class Progressbar:
-    def __init__(self, tqdm: _tqdm.tqdm | None) -> None:
+    def __init__(self, tqdm: ProgressBarTqdm) -> None:
         self._tqdm = tqdm
 
     def update_total(self, n: int) -> None:
@@ -24,12 +32,19 @@ def __enter__(self) -> "Progressbar":
             self._tqdm.__enter__()
         return self
 
-    def __exit__(self, typ, value, traceback) -> None:
+    def __exit__(
+        self,
+        typ: type[BaseException] | None,
+        value: BaseException | None,
+        traceback: TracebackType | None,
+    ) -> None:
         if self._tqdm is not None:
             self._tqdm.__exit__(typ, value, traceback)
 
 
-def progress(it: typing.Iterable, *, unit="pkg", **kwargs: typing.Any) -> typing.Any:
+def progress(
+    it: typing.Iterable[typing.Any], *, unit: str = "pkg", **kwargs: typing.Any
+) -> typing.Any:
     """tqdm progress bar"""
     if not sys.stdout.isatty():
         # wider progress bar in CI
@@ -37,7 +52,9 @@ def progress(it: typing.Iterable, *, unit="pkg", **kwargs: typing.Any) -> typing
     yield from _tqdm.tqdm(it, unit=unit, **kwargs)
 
 
-def progress_context(total: int, *, unit="pkg", **kwargs: typing.Any) -> Progressbar:
+def progress_context(
+    total: int, *, unit: str = "pkg", **kwargs: typing.Any
+) -> Progressbar:
     """Context manager for progress bar with dynamic updates"""
     if not sys.stdout.isatty():
         # wider progress bar in CI