diff --git a/apps/desktop/src/lib/trpc/routers/projects/projects.ts b/apps/desktop/src/lib/trpc/routers/projects/projects.ts
index bd5da74b855..0a015043544 100644
--- a/apps/desktop/src/lib/trpc/routers/projects/projects.ts
+++ b/apps/desktop/src/lib/trpc/routers/projects/projects.ts
@@ -17,7 +17,11 @@ import { PROJECT_COLOR_VALUES } from "shared/constants/project-colors";
 import simpleGit from "simple-git";
 import { z } from "zod";
 import { publicProcedure, router } from "../..";
-import { getDefaultBranch, getGitRoot } from "../workspaces/utils/git";
+import {
+	getDefaultBranch,
+	getGitRoot,
+	refreshDefaultBranch,
+} from "../workspaces/utils/git";
 import { assignRandomColor } from "./utils/colors";
 
 type Project = SelectProject;
@@ -253,10 +257,22 @@ export const createProjectsRouter = (getWindow: () => BrowserWindow | null) => {
 						branches = branchList.map((name) => ({ name, lastCommitDate: 0 }));
 					}
 
-					// Determine default branch
-					let defaultBranch = project.defaultBranch;
-					if (!defaultBranch) {
-						defaultBranch = await getDefaultBranch(project.mainRepoPath);
+					// Sync with remote in case the default branch changed (e.g. master -> main)
+					const remoteDefaultBranch = await refreshDefaultBranch(
+						project.mainRepoPath,
+					);
+
+					const defaultBranch =
+						remoteDefaultBranch ||
+						project.defaultBranch ||
+						(await getDefaultBranch(project.mainRepoPath));
+
+					if (defaultBranch !== project.defaultBranch) {
+						localDb
+							.update(projects)
+							.set({ defaultBranch })
+							.where(eq(projects.id, input.projectId))
+							.run();
 					}
 
 					// Sort: default branch first, then by date
@@ -581,6 +597,54 @@ export const createProjectsRouter = (getWindow: () => BrowserWindow | null) => {
 				return { success: true };
 			}),
 
+		refreshDefaultBranch: publicProcedure
+			.input(z.object({ id: z.string() }))
+			.mutation(async ({ input }) => {
+				const project = localDb
+					.select()
+					.from(projects)
+					.where(eq(projects.id, input.id))
+					.get();
+
+				if (!project) {
+					throw new Error(`Project ${input.id} not found`);
+				}
+
+				const remoteDefaultBranch = await refreshDefaultBranch(
+					project.mainRepoPath,
+				);
+
+				if (
+					remoteDefaultBranch &&
+					remoteDefaultBranch !== project.defaultBranch
+				) {
+					localDb
+						.update(projects)
+						.set({ defaultBranch: remoteDefaultBranch })
+						.where(eq(projects.id, input.id))
+						.run();
+
+					return {
+						success: true,
+						defaultBranch: remoteDefaultBranch,
+						changed: true,
+						previousBranch: project.defaultBranch,
+					};
+				}
+
+				// Ensure we always return a valid default branch
+				const defaultBranch =
+					project.defaultBranch ??
+					remoteDefaultBranch ??
+					(await getDefaultBranch(project.mainRepoPath));
+
+				return {
+					success: true,
+					defaultBranch,
+					changed: false,
+				};
+			}),
+
 		close: publicProcedure
 			.input(z.object({ id: z.string() }))
 			.mutation(async ({ input }) => {
diff --git a/apps/desktop/src/lib/trpc/routers/workspaces/utils/git.ts b/apps/desktop/src/lib/trpc/routers/workspaces/utils/git.ts
index ddd43e51711..6e48931dcc0 100644
--- a/apps/desktop/src/lib/trpc/routers/workspaces/utils/git.ts
+++ b/apps/desktop/src/lib/trpc/routers/workspaces/utils/git.ts
@@ -322,6 +322,49 @@ export async function fetchDefaultBranch(
 	return commit.trim();
 }
 
+/**
+ * Refreshes the local origin/HEAD symref from the remote and returns the current default branch.
+ * This detects when the remote repository's default branch has changed (e.g., master -> main).
+ * @param mainRepoPath - Path to the main repository
+ * @returns The current default branch name, or null if unable to determine
+ */
+export async function refreshDefaultBranch(
+	mainRepoPath: string,
+): Promise<string | null> {
+	const git = simpleGit(mainRepoPath);
+
+	const hasRemote = await hasOriginRemote(mainRepoPath);
+	if (!hasRemote) {
+		return null;
+	}
+
+	try {
+		// Git doesn't auto-update origin/HEAD on fetch, so we must explicitly
+		// sync it to detect when the remote's default branch changes
+		await git.remote(["set-head", "origin", "--auto"]);
+
+		const headRef = await git.raw(["symbolic-ref", "refs/remotes/origin/HEAD"]);
+		const match = headRef.trim().match(/refs\/remotes\/origin\/(.+)/);
+		if (match) {
+			return match[1];
+		}
+	} catch {
+		// set-head requires network access; fall back to ls-remote which may
+		// work in some edge cases or provide a more specific error
+		try {
+			const result = await git.raw(["ls-remote", "--symref", "origin", "HEAD"]);
+			const symrefMatch = result.match(/ref:\s+refs\/heads\/(.+?)\tHEAD/);
+			if (symrefMatch) {
+				return symrefMatch[1];
+			}
+		} catch {
+			// Network unavailable - caller will use cached value
+		}
+	}
+
+	return null;
+}
+
 export async function checkNeedsRebase(
 	worktreePath: string,
 	defaultBranch: string,
diff --git a/apps/desktop/src/lib/trpc/routers/workspaces/workspaces.ts b/apps/desktop/src/lib/trpc/routers/workspaces/workspaces.ts
index 21705214431..bd729ed299e 100644
--- a/apps/desktop/src/lib/trpc/routers/workspaces/workspaces.ts
+++ b/apps/desktop/src/lib/trpc/routers/workspaces/workspaces.ts
@@ -27,6 +27,7 @@ import {
 	hasUncommittedChanges,
 	hasUnpushedCommits,
 	listBranches,
+	refreshDefaultBranch,
 	removeWorktree,
 	safeCheckoutBranch,
 	worktreeExists,
@@ -67,11 +68,17 @@ export const createWorkspacesRouter = () => {
 					branch,
 				);
 
-				// Get default branch (lazy migration for existing projects without defaultBranch)
-				let defaultBranch = project.defaultBranch;
-				if (!defaultBranch) {
-					defaultBranch = await getDefaultBranch(project.mainRepoPath);
-					// Save it for future use
+				// Sync with remote in case the default branch changed (e.g. master -> main)
+				const remoteDefaultBranch = await refreshDefaultBranch(
+					project.mainRepoPath,
+				);
+
+				const defaultBranch =
+					remoteDefaultBranch ||
+					project.defaultBranch ||
+					(await getDefaultBranch(project.mainRepoPath));
+
+				if (defaultBranch !== project.defaultBranch) {
 					localDb
 						.update(projects)
 						.set({ defaultBranch })
@@ -79,7 +86,6 @@ export const createWorkspacesRouter = () => {
 						.run();
 				}
 
-				// Use provided baseBranch or fall back to default
 				const targetBranch = input.baseBranch || defaultBranch;
 
 				// Check if this repo has a remote origin
@@ -1058,11 +1064,20 @@ export const createWorkspacesRouter = () => {
 					throw new Error(`Project ${workspace.projectId} not found`);
 				}
 
-				// Get default branch (lazy migration for existing projects without defaultBranch)
+				// Sync with remote in case the default branch changed (e.g. master -> main)
+				const remoteDefaultBranch = await refreshDefaultBranch(
+					project.mainRepoPath,
+				);
+
 				let defaultBranch = project.defaultBranch;
 				if (!defaultBranch) {
 					defaultBranch = await getDefaultBranch(project.mainRepoPath);
-					// Save it for future use
+				}
+				if (remoteDefaultBranch && remoteDefaultBranch !== defaultBranch) {
+					defaultBranch = remoteDefaultBranch;
+				}
+
+				if (defaultBranch !== project.defaultBranch) {
 					localDb
 						.update(projects)
 						.set({ defaultBranch })
@@ -1092,7 +1107,7 @@ export const createWorkspacesRouter = () => {
 					.where(eq(worktrees.id, worktree.id))
 					.run();
 
-				return { gitStatus };
+				return { gitStatus, defaultBranch };
 			}),
 
 		getGitHubStatus: publicProcedure