diff --git a/internal/cmd/done.go b/internal/cmd/done.go
index 45f55f77..c841e63c 100644
--- a/internal/cmd/done.go
+++ b/internal/cmd/done.go
@@ -164,13 +164,16 @@ func runDone(cmd *cobra.Command, args []string) error {
 			return fmt.Errorf("branch has %d unpushed commit(s); run 'git push -u origin %s' first", unpushedCount, branch)
 		}
 
-		// Check that branch has commits ahead of main (prevents submitting stale branches)
-		aheadCount, err := g.CommitsAhead("main", branch)
+		// Detect the repo's default branch (main vs master)
+		defaultBranch := g.RemoteDefaultBranch()
+
+		// Check that branch has commits ahead of default branch (prevents submitting stale branches)
+		aheadCount, err := g.CommitsAhead(defaultBranch, branch)
 		if err != nil {
-			return fmt.Errorf("checking commits ahead of main: %w", err)
+			return fmt.Errorf("checking commits ahead of %s: %w", defaultBranch, err)
 		}
 		if aheadCount == 0 {
-			return fmt.Errorf("branch '%s' has 0 commits ahead of main; nothing to merge", branch)
+			return fmt.Errorf("branch '%s' has 0 commits ahead of %s; nothing to merge", branch, defaultBranch)
 		}
 
 		if issueID == "" {
@@ -181,7 +184,7 @@ func runDone(cmd *cobra.Command, args []string) error {
 		bd := beads.New(cwd)
 
 		// Determine target branch (auto-detect integration branch if applicable)
-		target := "main"
+		target := defaultBranch
 		autoTarget, err := detectIntegrationBranch(bd, g, issueID)
 		if err == nil && autoTarget != "" {
 			target = autoTarget
diff --git a/internal/git/git.go b/internal/git/git.go
index e04d9998..28ff3ac5 100644
--- a/internal/git/git.go
+++ b/internal/git/git.go
@@ -255,6 +255,36 @@ func (g *Git) DefaultBranch() string {
 	return "main"
 }
 
+// RemoteDefaultBranch returns the default branch from the remote (origin).
+// This is useful in worktrees where HEAD may not reflect the repo's actual default.
+// Checks origin/HEAD first, then falls back to checking if master/main exists.
+// Returns "main" as final fallback.
+func (g *Git) RemoteDefaultBranch() string {
+	// Try to get from origin/HEAD symbolic ref
+	out, err := g.run("symbolic-ref", "refs/remotes/origin/HEAD")
+	if err == nil && out != "" {
+		// Returns refs/remotes/origin/main -> extract branch name
+		parts := strings.Split(out, "/")
+		if len(parts) > 0 {
+			return parts[len(parts)-1]
+		}
+	}
+
+	// Fallback: check if origin/master exists
+	_, err = g.run("rev-parse", "--verify", "origin/master")
+	if err == nil {
+		return "master"
+	}
+
+	// Fallback: check if origin/main exists
+	_, err = g.run("rev-parse", "--verify", "origin/main")
+	if err == nil {
+		return "main"
+	}
+
+	return "main" // final fallback
+}
+
 // HasUncommittedChanges returns true if there are uncommitted changes.
 func (g *Git) HasUncommittedChanges() (bool, error) {
 	status, err := g.Status()