diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index db7fd87b6b..a45b4a0508 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -1833,7 +1833,7 @@ _git_mergetool ()
 		return
 		;;
 	--*)
-		__gitcomp "--tool= --prompt --no-prompt"
+		__gitcomp "--tool= --prompt --no-prompt --gui --no-gui"
 		return
 		;;
 	esac