diff --git a/mpas_analysis/shared/io/write_netcdf.py b/mpas_analysis/shared/io/write_netcdf.py
index ac9e12658..b16c57767 100644
--- a/mpas_analysis/shared/io/write_netcdf.py
+++ b/mpas_analysis/shared/io/write_netcdf.py
@@ -42,7 +42,8 @@ def write_netcdf(ds, fileName, fillValues=netCDF4.default_fillvals):  # {{{
 
     '''
     encodingDict = {}
-    for variableName in ds:
+    variableNames = list(ds.data_vars.keys()) + list(ds.coords.keys())
+    for variableName in variableNames:
         dtype = ds[variableName].dtype
         for fillType in fillValues:
             if dtype == numpy.dtype(fillType):