diff --git a/nansat/mappers/sentinel1.py b/nansat/mappers/sentinel1.py
index 2491b758..57e7faba 100644
--- a/nansat/mappers/sentinel1.py
+++ b/nansat/mappers/sentinel1.py
@@ -1,4 +1,5 @@
 import json
+import logging
 import numpy as np
 from dateutil.parser import parse
 try:
@@ -154,6 +155,9 @@ def test2(gcp_dim):
 
         gcp_y, gcp_x = test1(gcp_y, gcp_x)
 
+        logging.debug("GCPY size: %d" % gcp_y)
+        logging.debug("GCPX size: %d" % gcp_x)
+
         if gcp_y*gcp_x != pixel.size:
             raise ValueError("GCP dimension mismatch")