diff --git a/MANIFEST.in b/MANIFEST.in
index 2d1a31b..c417490 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -38,3 +38,5 @@ include README.rst
 include CITATION.cff
 include isl/LICENSE
 include isl/imath/LICENSE
+
+recursive-exclude preproc-headers *