diff --git a/MANIFEST.in b/MANIFEST.in
index 6bfc3e3..cf27575 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -1,4 +1,4 @@
-include cwcwidth/_impl.pyx cwcwidth/wcwidth.c cwcwidth/wcwidth_compat.h
+include cwcwidth/_impl.pyx cwcwidth/_impl.c cwcwidth/wcwidth.c cwcwidth/wcwidth_compat.h
 include cwcwidth/_impl.pyi cwcwidth/py.typed
 recursive-include tests *.py
 include CHANGELOG.md