diff --git a/kwant/plotter.py b/kwant/plotter.py
index 0da459ed92b3b8178685740bc86934be15f8c50e..517ebd2ba0328223f3aadc860d43dac3909d2331 100644
--- a/kwant/plotter.py
+++ b/kwant/plotter.py
@@ -37,7 +37,7 @@ try:
     except ImportError:
         warnings.warn("3D plotting not available.", RuntimeWarning)
 except ImportError:
-    warnings.warn("matplotlib is not available, only iterator-providing"
+    warnings.warn("matplotlib is not available, only iterator-providing "
                   "functions will work.", RuntimeWarning)
     _mpl_enabled = False