diff --git a/mo/csv.py b/mo/csv.py
index 39051bcd517139d796e915a8c9991a0d448f841d..e7008e9b8514bab55ab13baf1277155568364691 100644
--- a/mo/csv.py
+++ b/mo/csv.py
@@ -123,7 +123,7 @@ def read(file: IO, fmt: FileFormat, row_class: Type[Row]):
             if not any(h in columns for h in header):
                 raise MissingHeaderError()
             for h in header:
-                if not h in columns:
+                if h not in columns:
                     best_matches = difflib.get_close_matches(h, columns, n=1, cutoff=0.8)
                     if best_matches:
                         warnings.append(