diff --git a/saqc/lib/ts_operators.py b/saqc/lib/ts_operators.py
index e63eb8b7481b982901529882e79879b837b3edf5..b18ad156081c2e3f24f6b0b3a1960b638929c14a 100644
--- a/saqc/lib/ts_operators.py
+++ b/saqc/lib/ts_operators.py
@@ -310,7 +310,7 @@ def interpolateNANs(
     else:
         gap_mask = (
             gap_mask.replace(True, np.nan)
-            .fillna(method="bfill", limit=inter_limit)
+            .fillna(method="bfill", limit=inter_limit-1)
             .replace(np.nan, True)
             .astype(bool)
         )