--- a/Plugins/VcsPlugins/vcsMercurial/BookmarksExtension/HgBookmarkRenameDialog.py	Tue Mar 18 19:23:35 2014 +0100
+++ b/Plugins/VcsPlugins/vcsMercurial/BookmarksExtension/HgBookmarkRenameDialog.py	Wed Mar 19 19:26:30 2014 +0100
@@ -65,4 +65,7 @@
         @return tuple naming the new and old bookmark names
             (string, string)
         """
-        return self.nameEdit.text(), self.bookmarkCombo.currentText()
+        return (
+            self.nameEdit.text().replace(" ", "_"),
+            self.bookmarkCombo.currentText().replace(" ", "_")
+        )