diff --git a/pandas/io/pytables.py b/pandas/io/pytables.py
index 854843ffdd152..dff2c6f0df7b1 100644
--- a/pandas/io/pytables.py
+++ b/pandas/io/pytables.py
@@ -2517,7 +2517,9 @@ def write_array(self, key, value, items=None):
         transposed = False
 
         if com.is_categorical_dtype(value):
-            raise NotImplementedError("cannot store a category dtype")
+            raise NotImplementedError('Cannot store a category dtype in '
+                                      'a HDF5 dataset that uses format='
+                                      '"fixed". Use format="table".')
 
         if not empty_array:
             value = value.T