diff --git a/cmd/bd/sync.go b/cmd/bd/sync.go
index 92ed856a..39d9b517 100644
--- a/cmd/bd/sync.go
+++ b/cmd/bd/sync.go
@@ -380,12 +380,20 @@ Use --merge to merge the sync branch back to main branch.`,
 		if err := ensureStoreActive(); err == nil && store != nil {
 			syncBranchName, _ = syncbranch.Get(ctx, store)
 			if syncBranchName != "" && syncbranch.HasGitRemote(ctx) {
-				repoRoot, err = syncbranch.GetRepoRoot(ctx)
-				if err != nil {
-					fmt.Fprintf(os.Stderr, "Warning: sync.branch configured but failed to get repo root: %v\n", err)
-					fmt.Fprintf(os.Stderr, "Falling back to current branch commits\n")
+				// GH#519: Check if sync.branch equals current branch
+				// If so, we can't use a worktree (git doesn't allow same branch in multiple worktrees)
+				// Fall back to direct commits on the current branch
+				if syncbranch.IsSyncBranchSameAsCurrent(ctx, syncBranchName) {
+					// sync.branch == current branch - use regular commits, not worktree
+					useSyncBranch = false
 				} else {
-					useSyncBranch = true
+					repoRoot, err = syncbranch.GetRepoRoot(ctx)
+					if err != nil {
+						fmt.Fprintf(os.Stderr, "Warning: sync.branch configured but failed to get repo root: %v\n", err)
+						fmt.Fprintf(os.Stderr, "Falling back to current branch commits\n")
+					} else {
+						useSyncBranch = true
+					}
 				}
 			}
 		}
diff --git a/internal/syncbranch/worktree.go b/internal/syncbranch/worktree.go
index de272575..88d3da7c 100644
--- a/internal/syncbranch/worktree.go
+++ b/internal/syncbranch/worktree.go
@@ -916,3 +916,25 @@ func HasGitRemote(ctx context.Context) bool {
 	}
 	return len(strings.TrimSpace(string(output))) > 0
 }
+
+// GetCurrentBranch returns the name of the current git branch
+func GetCurrentBranch(ctx context.Context) (string, error) {
+	cmd := exec.CommandContext(ctx, "git", "symbolic-ref", "--short", "HEAD")
+	output, err := cmd.Output()
+	if err != nil {
+		return "", fmt.Errorf("failed to get current branch: %w", err)
+	}
+	return strings.TrimSpace(string(output)), nil
+}
+
+// IsSyncBranchSameAsCurrent returns true if the sync branch is the same as the current branch.
+// This is used to detect the case where we can't use a worktree because the branch is already
+// checked out. In this case, we should commit directly to the current branch instead.
+// See: https://github.com/steveyegge/beads/issues/519
+func IsSyncBranchSameAsCurrent(ctx context.Context, syncBranch string) bool {
+	currentBranch, err := GetCurrentBranch(ctx)
+	if err != nil {
+		return false
+	}
+	return currentBranch == syncBranch
+}
diff --git a/internal/syncbranch/worktree_divergence_test.go b/internal/syncbranch/worktree_divergence_test.go
index 96289e57..99060477 100644
--- a/internal/syncbranch/worktree_divergence_test.go
+++ b/internal/syncbranch/worktree_divergence_test.go
@@ -683,3 +683,70 @@ func TestCountIssuesInContent(t *testing.T) {
 		})
 	}
 }
+
+// TestIsSyncBranchSameAsCurrent tests detection of sync.branch == current branch (GH#519)
+func TestIsSyncBranchSameAsCurrent(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping integration test in short mode")
+	}
+
+	ctx := context.Background()
+
+	t.Run("returns true when sync branch equals current branch", func(t *testing.T) {
+		repoDir := setupTestRepo(t)
+		defer os.RemoveAll(repoDir)
+
+		// Create initial commit so we can get current branch
+		writeFile(t, filepath.Join(repoDir, ".beads", "issues.jsonl"), `{"id":"test-1"}`)
+		runGit(t, repoDir, "add", ".")
+		runGit(t, repoDir, "commit", "-m", "initial commit")
+
+		// Get current branch name
+		currentBranch := strings.TrimSpace(getGitOutput(t, repoDir, "symbolic-ref", "--short", "HEAD"))
+
+		// Save original dir and change to test repo
+		origDir, _ := os.Getwd()
+		os.Chdir(repoDir)
+		defer os.Chdir(origDir)
+
+		// Should return true when sync branch == current branch
+		if !IsSyncBranchSameAsCurrent(ctx, currentBranch) {
+			t.Errorf("IsSyncBranchSameAsCurrent(%q) = false, want true", currentBranch)
+		}
+	})
+
+	t.Run("returns false when sync branch differs from current branch", func(t *testing.T) {
+		repoDir := setupTestRepo(t)
+		defer os.RemoveAll(repoDir)
+
+		// Create initial commit
+		writeFile(t, filepath.Join(repoDir, ".beads", "issues.jsonl"), `{"id":"test-1"}`)
+		runGit(t, repoDir, "add", ".")
+		runGit(t, repoDir, "commit", "-m", "initial commit")
+
+		// Save original dir and change to test repo
+		origDir, _ := os.Getwd()
+		os.Chdir(repoDir)
+		defer os.Chdir(origDir)
+
+		// Should return false when sync branch != current branch
+		if IsSyncBranchSameAsCurrent(ctx, "beads-sync") {
+			t.Error("IsSyncBranchSameAsCurrent(\"beads-sync\") = true, want false")
+		}
+	})
+
+	t.Run("returns false on error getting current branch", func(t *testing.T) {
+		// Test in a non-git directory
+		tmpDir, _ := os.MkdirTemp("", "non-git-*")
+		defer os.RemoveAll(tmpDir)
+
+		origDir, _ := os.Getwd()
+		os.Chdir(tmpDir)
+		defer os.Chdir(origDir)
+
+		// Should return false when not in a git repo
+		if IsSyncBranchSameAsCurrent(ctx, "any-branch") {
+			t.Error("IsSyncBranchSameAsCurrent in non-git dir = true, want false")
+		}
+	})
+}