diff --git a/skimage/io/_plugins/pil_plugin.py b/skimage/io/_plugins/pil_plugin.py
index 218a9903..751194e5 100644
--- a/skimage/io/_plugins/pil_plugin.py
+++ b/skimage/io/_plugins/pil_plugin.py
@@ -33,8 +33,8 @@ def imread(fname, dtype=None):
         # this will raise an IOError if the file is not readable
         im.getdata()[0]
     except IOError:
-        raise ValueError('Could not load "%s": make sure you have library '
-            'support for "%s" files' % (fname, im.format))
+        raise ValueError('Could not load "%s": make sure you have external library '
+            'installed for "%s" files' % (fname, im.format))
     else:
         return pil_to_ndarray(im, dtype)