diff --git a/tests/python/ipnbdoctest.py b/tests/python/ipnbdoctest.py
index 5d7d00d10..cdf4a4407 100755
--- a/tests/python/ipnbdoctest.py
+++ b/tests/python/ipnbdoctest.py
@@ -180,21 +180,41 @@ def canonical_dict(dict, ignores):
     return dict
 
 
+def keep_dict(dict):
+    # pandas imports Matplotlib, which can display a message about building the
+    # the font cache if it does not exist, and if doing so takes more than 5
+    # seconds.   Just ignore those.
+    if ('name' in dict and dict['name'] == 'stderr' and
+        type(dict['text']) is str and
+        dict['text'].startswith("Matplotlib is building the font cache")):
+        return False
+    return True
+
+
 def compare_outputs(ref, test, ignores=[]):
     '''Check that two lists of outputs are equivalent and report the
     result.'''
 
+    cref = [canonical_dict(d, ignores) for d in ref if keep_dict(d)]
+    ctest = [canonical_dict(d, ignores) for d in test if keep_dict(d)]
+
+    ok = True
+
+    if len(cref) != len(ctest):
+        print("output length mismatch (expected {}, got {})".format(
+            len(cref), len(ctest)))
+        ok = False
     # There can be several outputs.  For instance wnen the cell both
     # prints a result (goes to "stdout") and displays an automaton
     # (goes to "data").
-    exp = pprint.pformat([canonical_dict(d, ignores) for d in ref],  width=132)
-    eff = pprint.pformat([canonical_dict(d, ignores) for d in test], width=132)
+    exp = pprint.pformat(cref, width=132)
+    eff = pprint.pformat(ctest, width=132)
     if exp[:-1] != '\n':
         exp += '\n'
     if eff[:-1] != '\n':
         eff += '\n'
     if exp == eff:
-        return True
+        return ok
     else:
         print(''.join(diff(exp.splitlines(1), eff.splitlines(1),
                            fromfile='expected', tofile='effective')))
@@ -296,10 +316,6 @@ def test_notebook(ipynb):
             continue
 
         failed = False
-        if len(outs) != len(cell.outputs):
-            print("output length mismatch (expected {}, got {})".format(
-                  len(cell.outputs), len(outs)))
-            failed = True
         if not compare_outputs(cell.outputs, outs):
             failed = True
         print("cell %d: " % i, end="")