diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
index 354e3db880b4..430d6112780b 100644
--- a/lib/matplotlib/ticker.py
+++ b/lib/matplotlib/ticker.py
@@ -411,6 +411,10 @@ class FormatStrFormatter(Formatter):
 
     The format string should have a single variable format (%) in it.
     It will be applied to the value (not the position) of the tick.
+
+    Negative numeric values will use a dash not a unicode minus,
+    use mathtext to get a unicode minus by wrappping the format specifier
+    with $ (e.g. "$%g$").
     """
     def __init__(self, fmt):
         self.fmt = fmt