diff --git a/Documentation/git-worktree.txt b/Documentation/git-worktree.txt
index 41585f535dba76..5d54f36a7134f4 100644
--- a/Documentation/git-worktree.txt
+++ b/Documentation/git-worktree.txt
@@ -61,8 +61,13 @@ $ git worktree add --track -b <branch> <path> <remote>/<branch>
 ------------
 +
 If `<commit-ish>` is omitted and neither `-b` nor `-B` nor `--detach` used,
-then, as a convenience, a new branch based at HEAD is created automatically,
-as if `-b $(basename <path>)` was specified.
+then, as a convenience, the new worktree is associated with a branch
+(call it `<branch>`) named after `$(basename <path>)`.  If `<branch>`
+doesn't exist, a new branch based on HEAD is automatically created as
+if `-b <branch>` was given.  If `<branch>` does exist, it will be
+checked out in the new worktree, if it's not checked out anywhere
+else, otherwise the command will refuse to create the worktree (unless
+`--force` is used).
 
 list::
 
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 6bd32b6090967b..d3aeb4877dbd1f 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -391,8 +391,17 @@ static const char *dwim_branch(const char *path, const char **new_branch)
 {
 	int n;
 	const char *s = worktree_basename(path, &n);
-	*new_branch = xstrndup(s, n);
-	UNLEAK(*new_branch);
+	const char *branchname = xstrndup(s, n);
+	struct strbuf ref = STRBUF_INIT;
+
+	UNLEAK(branchname);
+	if (!strbuf_check_branch_ref(&ref, branchname) &&
+	    ref_exists(ref.buf)) {
+		strbuf_release(&ref);
+		return branchname;
+	}
+
+	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
 		const char *remote =
diff --git a/t/t2025-worktree-add.sh b/t/t2025-worktree-add.sh
index 2b959449730e14..ad38507d000a52 100755
--- a/t/t2025-worktree-add.sh
+++ b/t/t2025-worktree-add.sh
@@ -198,13 +198,25 @@ test_expect_success '"add" with <branch> omitted' '
 	test_cmp_rev HEAD bat
 '
 
-test_expect_success '"add" auto-vivify does not clobber existing branch' '
-	test_commit c1 &&
-	test_commit c2 &&
-	git branch precious HEAD~1 &&
-	test_must_fail git worktree add precious &&
-	test_cmp_rev HEAD~1 precious &&
-	test_path_is_missing precious
+test_expect_success '"add" checks out existing branch of dwimd name' '
+	git branch dwim HEAD~1 &&
+	git worktree add dwim &&
+	test_cmp_rev HEAD~1 dwim &&
+	(
+		cd dwim &&
+		test_cmp_rev HEAD dwim
+	)
+'
+
+test_expect_success '"add <path>" dwim fails with checked out branch' '
+	git checkout -b test-branch &&
+	test_must_fail git worktree add test-branch &&
+	test_path_is_missing test-branch
+'
+
+test_expect_success '"add --force" with existing dwimd name doesnt die' '
+	git checkout test-branch &&
+	git worktree add --force test-branch
 '
 
 test_expect_success '"add" no auto-vivify with --detach and <branch> omitted' '