diff --git a/IPython/utils/tests/test_text.py b/IPython/utils/tests/test_text.py
index 8822262..fa4c7fb 100644
--- a/IPython/utils/tests/test_text.py
+++ b/IPython/utils/tests/test_text.py
@@ -149,6 +149,9 @@ def test_long_substr2():
     data = ['abc', 'abd', 'abf', 'ab']
     nt.assert_equals(text.long_substr(data), 'ab')
 
+def test_long_substr_empty():
+    data = []
+    nt.assert_equals(text.long_substr(data), '')
 
 def test_strip_email():
     src = """\
diff --git a/IPython/utils/text.py b/IPython/utils/text.py
index f66962a..b53f826 100644
--- a/IPython/utils/text.py
+++ b/IPython/utils/text.py
@@ -553,7 +553,7 @@ def long_substr(data):
             for j in range(len(data[0])-i+1):
                 if j > len(substr) and all(data[0][i:i+j] in x for x in data):
                     substr = data[0][i:i+j]
-    else:
+    elif len(data) == 1:
         substr = data[0]
     return substr