diff --git a/xarray/core/dataset.py b/xarray/core/dataset.py
index a5f6376d399..7cc0b92ce8e 100644
--- a/xarray/core/dataset.py
+++ b/xarray/core/dataset.py
@@ -2912,7 +2912,7 @@ def reduce(self, func, dim=None, keep_attrs=None, numeric_only=False,
         else:
             dims = set(dim)
 
-        missing_dimensions = [dim for d in dims if d not in self.dims]
+        missing_dimensions = [d for d in dims if d not in self.dims]
         if missing_dimensions:
             raise ValueError('Dataset does not contain the dimensions: %s'
                              % missing_dimensions)
@@ -3711,7 +3711,7 @@ def quantile(self, q, dim=None, interpolation='linear',
         else:
             dims = set(dim)
 
-        _assert_empty([dim for d in dims if d not in self.dims],
+        _assert_empty([d for d in dims if d not in self.dims],
                       'Dataset does not contain the dimensions: %s')
 
         q = np.asarray(q, dtype=np.float64)