diff --git a/sandbox/grist/imports/import_csv.py b/sandbox/grist/imports/import_csv.py
index e71851f7..d3e80ee2 100644
--- a/sandbox/grist/imports/import_csv.py
+++ b/sandbox/grist/imports/import_csv.py
@@ -107,7 +107,7 @@ def _guess_dialect(file_obj):
   try:
     # Restrict allowed delimiters to prevent guessing other char than this list.
     dialect = csv.Sniffer().sniff(file_obj.read(100000), delimiters=['\t', ',', ';', '|'])
-    log.info("Guessed dialect %s" % dict(dialect.__dict__))
+    log.info("Guessed dialect %s", dict(dialect.__dict__))
     # Mimic messytables default for now.
     dialect.lineterminator = "\n"
     dialect.doublequote = True