diff --git a/py/stencila/schema/interpreter.py b/py/stencila/schema/interpreter.py
index 9b5d96494b..779e4ba707 100644
--- a/py/stencila/schema/interpreter.py
+++ b/py/stencila/schema/interpreter.py
@@ -40,12 +40,12 @@
 except ImportError:
     # pylint: disable=R0903
     class MPLFigure:  # type: ignore
-        """A fake MPLFigure to prevent RefenceErrors later."""
+        """A fake MPLFigure to prevent ReferenceErrors later."""
 
 
     # pylint: disable=R0903
     class MLPArtist:  # type: ignore
-        """A fake MLPArtist to prevent RefenceErrors later."""
+        """A fake MLPArtist to prevent ReferenceErrors later."""
 
 
     MPL_AVAILABLE = False
@@ -58,7 +58,7 @@ class MLPArtist:  # type: ignore
 except ImportError:
     # pylint: disable=R0903
     class DataFrame:  # type: ignore
-        """A fake DataFrame to prevent RefenceErrors later."""
+        """A fake DataFrame to prevent ReferenceErrors later."""
 
 
     PANDAS_AVAILABLE = False
@@ -383,12 +383,23 @@ def decode_output(self, output: typing.Any) -> typing.Any:
         Check if the output is convertible from a special data type to a Stencila type.
 
         If not, just return the original object."""
+
+        if isinstance(output, list):
+            return [self.decode_output(item) for item in output]
+
+        if isinstance(output, tuple):
+            return tuple(self.decode_output(item) for item in output)
+
         if self.value_is_mpl(output):
             return self.decode_mpl()
 
         if isinstance(output, DataFrame):
             return self.decode_dataframe(output)
 
+        if PANDAS_AVAILABLE:
+            if isinstance(output, numpy.ndarray):
+                return output.tolist()
+
         return output
 
 
diff --git a/py/stencila/schema/util.py b/py/stencila/schema/util.py
index 982df90128..edd5ba057d 100644
--- a/py/stencila/schema/util.py
+++ b/py/stencila/schema/util.py
@@ -8,6 +8,9 @@
 
 def to_dict(node: typing.Any) -> dict:
     """Convert an Entity node to a dictionary"""
+    if not isinstance(node, types.Entity):
+        return str(node)
+
     node_dict = {
         "type": node.__class__.__name__
     }