diff --git a/satpy/readers/insat3d_img_l1b_h5.py b/satpy/readers/insat3d_img_l1b_h5.py
index dede8aefcd..29f211f08f 100644
--- a/satpy/readers/insat3d_img_l1b_h5.py
+++ b/satpy/readers/insat3d_img_l1b_h5.py
@@ -179,7 +179,10 @@ def get_area_def(self, ds_id):
         #fov = self.datatree.attrs["Field_of_View(degrees)"]
         fov = 18
         cfac = 2 ** 16 / (fov / cols)
-        lfac = 2 ** 16 / (fov / lines)
+
+        # From reverse engineering metadata from a netcdf file, we discovered
+        # the lfac is actually the same as cfac, ie dependent on cols, not lines!
+        lfac = 2 ** 16 / (fov / cols)
 
         h = self.datatree.attrs["Observed_Altitude(km)"] * 1000
         # WGS 84
@@ -191,8 +194,8 @@ def get_area_def(self, ds_id):
         pdict = {
             "cfac": cfac,
             "lfac": lfac,
-            "coff": cols / 2,
-            "loff": lines / 2,
+            "coff": cols // 2 + 1,
+            "loff": lines // 2,
             "ncols": cols,
             "nlines": lines,
             "scandir": "N2S",
diff --git a/satpy/tests/reader_tests/test_insat3d_img_l1b_h5.py b/satpy/tests/reader_tests/test_insat3d_img_l1b_h5.py
index 7378078c2a..3b100415a4 100644
--- a/satpy/tests/reader_tests/test_insat3d_img_l1b_h5.py
+++ b/satpy/tests/reader_tests/test_insat3d_img_l1b_h5.py
@@ -280,6 +280,8 @@ def test_filehandler_returns_area(insat_filehandler):
     area_def = fh.get_area_def(ds_id)
     _ = area_def.get_lonlats(chunks=1000)
     assert subsatellite_longitude == area_def.crs.to_cf()["longitude_of_projection_origin"]
+    np.testing.assert_allclose(area_def.area_extent, [-5620072.101427, -5640108.009097,
+                                                      5620072.101427, 5644115.190631])
 
 
 def test_filehandler_has_start_and_end_time(insat_filehandler):