diff --git a/pysam/libcalignmentfile.pyi b/pysam/libcalignmentfile.pyi
index 30ed7e16..6f106af9 100644
--- a/pysam/libcalignmentfile.pyi
+++ b/pysam/libcalignmentfile.pyi
@@ -67,7 +67,7 @@ class AlignmentHeader:
     def lengths(self) -> Tuple[int]: ...
     def to_dict(self) -> Dict: ...
     def get_reference_name(self, tid: int) -> Optional[str]: ...
-    def get_reference_length(self, reference: int) -> int: ...
+    def get_reference_length(self, reference: str) -> int: ...
     def is_valid_tid(self, tid: int) -> bool: ...
     def get_tid(self, reference: str) -> int: ...