diff --git a/third_party/2and3/markdown/preprocessors.pyi b/third_party/2and3/markdown/preprocessors.pyi
index c29b6ab59623..e3083cdf5875 100644
--- a/third_party/2and3/markdown/preprocessors.pyi
+++ b/third_party/2and3/markdown/preprocessors.pyi
@@ -1,14 +1,14 @@
-from typing import Any, Pattern
+from typing import Any, Iterable, List, Pattern
 
 from . import util
 
 def build_preprocessors(md, **kwargs): ...
 
 class Preprocessor(util.Processor):
-    def run(self, lines) -> None: ...
+    def run(self, lines: List[str]) -> List[str]: ...
 
 class NormalizeWhitespace(Preprocessor):
-    def run(self, lines): ...
+    def run(self, lines: Iterable[str]) -> List[str]: ...
 
 class HtmlBlockPreprocessor(Preprocessor):
     right_tag_patterns: Any
@@ -17,10 +17,10 @@ class HtmlBlockPreprocessor(Preprocessor):
     attrs_re: Any
     left_tag_re: Any
     markdown_in_raw: bool = ...
-    def run(self, lines): ...
+    def run(self, lines: Iterable[str]) -> List[str]: ...
 
 class ReferencePreprocessor(Preprocessor):
     TITLE: str = ...
     RE: Pattern
     TITLE_RE: Pattern
-    def run(self, lines): ...
+    def run(self, lines: List[str]) -> List[str]: ...