diff --git a/git-checkout.sh b/git-checkout.sh
index 679057dcbf..855cf46a2d 100755
--- a/git-checkout.sh
+++ b/git-checkout.sh
@@ -150,35 +150,32 @@ fi
 # correct, it feels somewhat funny.  More importantly, we do not
 # want "git checkout" nor "git checkout -f" to detach HEAD.
 
+detached=
+detach_warn=
+
 if test -z "$branch$newbranch" && test "$new" != "$old"
 then
-	# NEEDSWORK: we would want to have a command here
-	# that allows us to detach the HEAD atomically.  Perhaps
-	# something like "git update-ref --detach HEAD $new"
-	echo "$new" >"$GIT_DIR/HEAD.new" &&
-	mv "$GIT_DIR/HEAD.new" "$GIT_DIR/HEAD" || die "Cannot detach HEAD"
-
+	detached="$new"
 	if test -n "$oldbranch"
 	then
-		echo >&2 "warning: you are not on ANY branch anymore.
+		detach_warn="warning: you are not on ANY branch anymore.
 If you meant to create a new branch from the commit, you need -b to
 associate a new branch with the wanted checkout.  Example:
-  git checkout -b <new_branch_name> $arg
-"
+  git checkout -b <new_branch_name> $arg"
 	fi
 elif test -z "$oldbranch" && test -n "$branch"
 then
 	# Coming back...
 	if test -z "$force"
 	then
-		mb=$(git merge-base --all $old $new) &&
-		case "$LF$mb$LF" in
-		*"$LF$old$LF"*)	: ;;
-		*)	false ;;
-		esac || {
+		git show-ref -d -s | grep "$old" >/dev/null || {
 			echo >&2 \
-"You are not on a branch and switching to $new_name branch may lose
-your changes.  Use 'git checkout -f $new_name' if you want to."
+"You are not on any branch and switching to branch '$new_name'
+may lose your changes.  At this point, you can do one of two things:
+ (1) Decide it is Ok and say 'git checkout -f $new_name';
+ (2) Start a new branch from the current commit, by saying
+     'git checkout -b <branch-name>'.
+Leaving your HEAD detached; not switching to branch '$new_name'."
 			exit 1;
 		}
 	fi
@@ -265,8 +262,25 @@ if [ "$?" -eq 0 ]; then
 		git-update-ref -m "checkout: Created from $new_name" "refs/heads/$newbranch" $new || exit
 		branch="$newbranch"
 	fi
-	[ "$branch" ] &&
-	GIT_DIR="$GIT_DIR" git-symbolic-ref HEAD "refs/heads/$branch"
+	if test -n "$branch"
+	then
+		GIT_DIR="$GIT_DIR" git-symbolic-ref HEAD "refs/heads/$branch"
+	elif test -n "$detached"
+	then
+		# NEEDSWORK: we would want a command to detach the HEAD
+		# atomically, instead of this handcrafted command sequence.
+		# Perhaps:
+		#	git update-ref --detach HEAD $new
+		# or something like that...
+		#
+		echo "$detached" >"$GIT_DIR/HEAD.new" &&
+		mv "$GIT_DIR/HEAD.new" "$GIT_DIR/HEAD" ||
+			die "Cannot detach HEAD"
+		if test -n "$detach_warn"
+		then
+			echo >&2 "$detach_warn"
+		fi
+	fi
 	rm -f "$GIT_DIR/MERGE_HEAD"
 else
 	exit 1