diff --git a/doc/make.py b/doc/make.py
index 55942734d712..783e159be23c 100755
--- a/doc/make.py
+++ b/doc/make.py
@@ -165,7 +165,7 @@ def all():
             os.unlink(link)
         else:
             raise RuntimeError("doc/{0} should be a directory or symlink -- it"
-                               " isn't")
+                               " isn't".format(link))
     if not os.path.exists(link):
         if hasattr(os, 'symlink'):
             os.symlink(target, link)