diff --git a/hgext/uncommit.py b/hgext/uncommit.py
--- a/hgext/uncommit.py
+++ b/hgext/uncommit.py
@@ -151,6 +151,9 @@
     files to their uncommitted state. This means that files modified or
     deleted in the changeset will be left unchanged, and so will remain
     modified in the working directory.
+
+    If no files are specified, the commit will be pruned, unless --keep is
+    given.
     """
     opts = pycompat.byteskwargs(opts)
 
diff --git a/tests/test-uncommit.t b/tests/test-uncommit.t
--- a/tests/test-uncommit.t
+++ b/tests/test-uncommit.t
@@ -27,6 +27,9 @@
       deleted in the changeset will be left unchanged, and so will remain
       modified in the working directory.
   
+      If no files are specified, the commit will be pruned, unless --keep is
+      given.
+  
   (use 'hg help -e uncommit' to show help for the uncommit extension)
   
   options ([+] can be repeated):