diff --git a/xarray/backends/netCDF4_.py b/xarray/backends/netCDF4_.py
index d26b2b5321e..8350183d5da 100644
--- a/xarray/backends/netCDF4_.py
+++ b/xarray/backends/netCDF4_.py
@@ -204,7 +204,9 @@ def _extract_nc4_variable_encoding(variable, raise_on_invalid=False,
         chunks_too_big = any(
             c > d and dim not in unlimited_dims
             for c, d, dim in zip(chunksizes, variable.shape, variable.dims))
-        changed_shape = encoding.get('original_shape') != variable.shape
+        has_original_shape = encoding.get('original_shape') is not None
+        changed_shape = (has_original_shape and
+                         encoding.get('original_shape') != variable.shape)
         if chunks_too_big or changed_shape:
             del encoding['chunksizes']