diff --git a/gridded_glm/libexec/_minute_gridder.py b/gridded_glm/libexec/_minute_gridder.py
index c24cb71b0ce9d44afd89d8d1dfb7653198ef4e55..16b997cc2971a328d3c2df9cd363424eea87a9e5 100644
--- a/gridded_glm/libexec/_minute_gridder.py
+++ b/gridded_glm/libexec/_minute_gridder.py
@@ -158,7 +158,9 @@ def get_outpath_base(args):
             start_time, end_time: datetimes that can be used with strftime syntax, e.g.
                 './{start_time:%y/%b/%d}/GLM_{start_time:%Y%m%d_%H%M%S}.nc'
     """
-    ops_environment, algorithm, platform, start_time, end_time, created_time = parse_glm_filename(os.path.basename(args.filenames[0]))
+    ordered_filenames = sorted(args.filenames)
+    _, _, platform, start_time, _, _ = parse_glm_filename(os.path.basename(ordered_filenames[0]))
+    _, _, _, _, end_time, _ = parse_glm_filename(os.path.basename(ordered_filenames[-1]))
 
     sector_short = get_sector_shortstring(args)
     mode = "M3" # FIXME: is GLM always in M3?