diff --git a/glmtools/io/glm.py b/glmtools/io/glm.py
index ac65fe6..af46984 100644
--- a/glmtools/io/glm.py
+++ b/glmtools/io/glm.py
@@ -552,8 +552,8 @@ def __init_fixed_grid_data(self):
         if ellipse_rev < 0:
             log.info("Inferring lightning ellipsoid from GLM product time")
             pt = self.dataset.product_time.dt
-            date = datetime(pt.year, pt.month, pt.day,
-                            pt.hour, pt.minute, pt.second)
+            date = datetime(pt.year.values, pt.month.values, pt.day.values,
+                            pt.hour.values, pt.minute.values, pt.second.values)
             ellipse_rev = ltg_ellpse_rev(date)
         log.info("Using lightning ellipsoid rev {0}".format(ellipse_rev))