diff --git a/py/_io/terminalwriter.py b/py/_io/terminalwriter.py
index 817bf2d8..be559867 100644
--- a/py/_io/terminalwriter.py
+++ b/py/_io/terminalwriter.py
@@ -227,7 +227,7 @@ def sep(self, sepchar, title=None, fullwidth=None, **kw):
             # i.e.    2 + 2*len(sepchar)*N + len(title) <= fullwidth
             #         2*len(sepchar)*N <= fullwidth - len(title) - 2
             #         N <= (fullwidth - len(title) - 2) // (2*len(sepchar))
-            N = (fullwidth - len(title) - 2) // (2*len(sepchar))
+            N = max((fullwidth - len(title) - 2) // (2*len(sepchar)), 1)
             fill = sepchar * N
             line = "%s %s %s" % (fill, title, fill)
         else:
diff --git a/testing/io_/test_terminalwriter.py b/testing/io_/test_terminalwriter.py
index 64b07568..1eef7f7d 100644
--- a/testing/io_/test_terminalwriter.py
+++ b/testing/io_/test_terminalwriter.py
@@ -165,6 +165,12 @@ def test_sep_with_title(self, tw):
         assert len(l) == 1
         assert l[0] == "-" * 26 + " hello " + "-" * (27-win32) + "\n"
 
+    def test_sep_longer_than_width(self, tw):
+        tw.sep('-', 'a' * 10, fullwidth=5)
+        line, = tw.getlines()
+        # even though the string is wider than the line, still have a separator
+        assert line == '- aaaaaaaaaa -\n'
+
     @py.test.mark.skipif("sys.platform == 'win32'")
     def test__escaped(self, tw):
         text2 = tw._escaped("hello", (31))