diff --git a/act/io/arm.py b/act/io/arm.py
index 05c9201a87..f9a7fc0cdf 100644
--- a/act/io/arm.py
+++ b/act/io/arm.py
@@ -841,12 +841,11 @@ def read_arm_mmcr(filenames):
     # read it in with xarray
     multi_ds = []
     for f in filenames:
-        nc = Dataset(f, 'a')
-        # Change heights name to range to read appropriately to xarray
-        if 'heights' in nc.dimensions:
-            nc.renameDimension('heights', 'range')
+        nc = Dataset(f, 'r')
         if nc is not None:
             ds = xr.open_dataset(xr.backends.NetCDF4DataStore(nc))
+            # Change heights name to range to read appropriately to xarray
+            ds = ds.rename_dims({"heights": "range"})
             multi_ds.append(ds)
     # Concatenate datasets together
     if len(multi_ds) > 1: