diff --git a/nansat/mappers/mapper_modis_l1.py b/nansat/mappers/mapper_modis_l1.py
index 6e72e9632..6db47543f 100644
--- a/nansat/mappers/mapper_modis_l1.py
+++ b/nansat/mappers/mapper_modis_l1.py
@@ -373,8 +373,8 @@ def __init__(self, filename, gdalDataset, gdalMetadata, GCP_COUNT=30, **kwargs):
         lons = gdal.Open(lonSubdataset).ReadAsArray()
         lats = gdal.Open(latSubdataset).ReadAsArray()
         gcps = []
-        rows = range(0, lons.shape[0], lons.shape[0]/GCP_COUNT)
-        cols = range(0, lons.shape[1], lons.shape[1]/GCP_COUNT)
+        rows = range(0, lons.shape[0], int(lons.shape[0]/GCP_COUNT))
+        cols = range(0, lons.shape[1], int(lons.shape[1]/GCP_COUNT))
         factor = self.dataset.RasterYSize / lons.shape[0]
         for r in rows:
             for c in cols: