diff --git a/python/cuml/cuml/feature_extraction/_vectorizers.py b/python/cuml/cuml/feature_extraction/_vectorizers.py
index 716b9fe631..272869ab90 100644
--- a/python/cuml/cuml/feature_extraction/_vectorizers.py
+++ b/python/cuml/cuml/feature_extraction/_vectorizers.py
@@ -213,11 +213,15 @@ def get_char_ngrams(self, ngram_size, str_series, doc_id_sr):
             tokens = str_series.str.tokenize(self.delimiter)
             del str_series
 
-            padding = Series(self.delimiter).repeat(len(tokens))
+            # tokens keeps the original per-document index (repeated per
+            # token); reset both to a plain range first so the two str.cat()
+            # calls below align positionally instead of by that index.
+            tokens = tokens.reset_index(drop=True)
+            padding = Series(self.delimiter).repeat(len(tokens)).reset_index(
+                drop=True
+            )
             tokens = tokens.str.cat(padding)
-            padding = padding.reset_index(drop=True)
             tokens = padding.str.cat(tokens)
-            tokens = tokens.reset_index(drop=True)
 
             ngram_sr = tokens.str.character_ngrams(n=ngram_size)