diff --git a/cmd/navigate.go b/cmd/navigate.go
index 52a94b9..c459a9d 100644
--- a/cmd/navigate.go
+++ b/cmd/navigate.go
@@ -68,26 +68,22 @@ func runNavigate(cfg *config.Config, delta int) error {
 
 	idx := s.IndexOf(currentBranch)
 	if idx < 0 {
-		// Might be on the trunk
-		if currentBranch == s.Trunk.Branch {
-			if delta > 0 && len(s.Branches) > 0 {
-				targetIdx := s.FirstActiveBranchIndex()
-				if targetIdx < 0 {
-					// All merged — fall back to top branch with warning
-					targetIdx = len(s.Branches) - 1
-					cfg.Warningf("Warning: all branches in this stack have been merged")
-				}
-				target := s.Branches[targetIdx].Branch
-				if err := git.CheckoutBranch(target); err != nil {
-					return err
-				}
-				cfg.Successf("Switched to %s", target)
-				return nil
+		// Current branch is the trunk (not in s.Branches).
+		// loadStack guarantees the branch is part of the stack.
+		if delta > 0 && len(s.Branches) > 0 {
+			targetIdx := s.FirstActiveBranchIndex()
+			if targetIdx < 0 {
+				targetIdx = len(s.Branches) - 1
+				cfg.Warningf("Warning: all branches in this stack have been merged")
 			}
-			cfg.Printf("Already at the bottom of the stack")
+			target := s.Branches[targetIdx].Branch
+			if err := git.CheckoutBranch(target); err != nil {
+				return err
+			}
+			cfg.Successf("Switched to %s", target)
 			return nil
 		}
-		cfg.Errorf("current branch %q is not in the stack", currentBranch)
+		cfg.Printf("Already at the bottom of the stack")
 		return nil
 	}
 
@@ -110,12 +106,7 @@ func runNavigate(cfg *config.Config, delta int) error {
 		}
 	} else {
 		// Build list of active (non-merged) branch indices
-		var activeIndices []int
-		for i, b := range s.Branches {
-			if !b.IsMerged() {
-				activeIndices = append(activeIndices, i)
-			}
-		}
+		activeIndices := s.ActiveBranchIndices()
 
 		// Find current position in active list
 		activePos := -1
diff --git a/internal/stack/stack.go b/internal/stack/stack.go
index f35c83d..ef7296b 100644
--- a/internal/stack/stack.go
+++ b/internal/stack/stack.go
@@ -124,6 +124,17 @@ func (s *Stack) FirstActiveBranchIndex() int {
 	return -1
 }
 
+// ActiveBranchIndices returns the indices of all non-merged branches.
+func (s *Stack) ActiveBranchIndices() []int {
+	var indices []int
+	for i, b := range s.Branches {
+		if !b.IsMerged() {
+			indices = append(indices, i)
+		}
+	}
+	return indices
+}
+
 // ActiveBaseBranch returns the effective parent for a branch, skipping merged
 // ancestors. For the first active branch (or any branch whose downstack is all
 // merged), this returns the trunk.
diff --git a/internal/stack/stack_test.go b/internal/stack/stack_test.go
index d20f1a3..3fa65de 100644
--- a/internal/stack/stack_test.go
+++ b/internal/stack/stack_test.go
@@ -192,6 +192,39 @@ func TestFirstActiveBranchIndex(t *testing.T) {
 	})
 }
 
+// --- ActiveBranchIndices: navigation ---
+
+func TestActiveBranchIndices(t *testing.T) {
+	t.Run("all active", func(t *testing.T) {
+		s := makeStack("main", "b1", "b2", "b3")
+		assert.Equal(t, []int{0, 1, 2}, s.ActiveBranchIndices())
+	})
+
+	t.Run("some merged", func(t *testing.T) {
+		s := Stack{
+			Trunk: BranchRef{Branch: "main"},
+			Branches: []BranchRef{
+				makeMergedBranch("b1", 1),
+				{Branch: "b2"},
+				makeMergedBranch("b3", 3),
+				{Branch: "b4"},
+			},
+		}
+		assert.Equal(t, []int{1, 3}, s.ActiveBranchIndices())
+	})
+
+	t.Run("all merged", func(t *testing.T) {
+		s := Stack{
+			Trunk: BranchRef{Branch: "main"},
+			Branches: []BranchRef{
+				makeMergedBranch("b1", 1),
+				makeMergedBranch("b2", 2),
+			},
+		}
+		assert.Empty(t, s.ActiveBranchIndices())
+	})
+}
+
 // --- Load / Save round-trip persistence ---
 
 func TestLoad_Save_RoundTrip(t *testing.T) {