diff --git a/backend/internal/service/project/service_test.go b/backend/internal/service/project/service_test.go
index 48e66a653..8088c9415 100644
--- a/backend/internal/service/project/service_test.go
+++ b/backend/internal/service/project/service_test.go
@@ -584,6 +584,16 @@ func configureCommitter(t *testing.T) {
 }
 
 func gitRepoWithCommit(t *testing.T, dir string) string {
+	t.Helper()
+	return gitRepoWithCommitWithOrigin(t, dir, "https://example.com/"+filepath.Base(dir)+".git")
+}
+
+func gitRepoWithCommitNoOrigin(t *testing.T, dir string) string {
+	t.Helper()
+	return gitRepoWithCommitWithOrigin(t, dir, "")
+}
+
+func gitRepoWithCommitWithOrigin(t *testing.T, dir, origin string) string {
 	t.Helper()
 	if out, err := exec.Command("git", "init", "-b", "main", dir).CombinedOutput(); err != nil {
 		t.Fatalf("git init: %v (%s)", err, out)
@@ -597,6 +607,11 @@ func gitRepoWithCommit(t *testing.T, dir string) string {
 	if out, err := exec.Command("git", "-C", dir, "commit", "-m", "initial").CombinedOutput(); err != nil {
 		t.Fatalf("git commit: %v (%s)", err, out)
 	}
+	if origin != "" {
+		if out, err := exec.Command("git", "-C", dir, "remote", "add", "origin", origin).CombinedOutput(); err != nil {
+			t.Fatalf("git remote add: %v (%s)", err, out)
+		}
+	}
 	return dir
 }
 
@@ -664,6 +679,17 @@ func TestManager_AddWorkspaceRejectsUncommittedChild(t *testing.T) {
 	wantCode(t, err, "WORKSPACE_CHILD_UNBORN")
 }
 
+func TestManager_AddWorkspaceRejectsChildWithoutOrigin(t *testing.T) {
+	configureCommitter(t)
+	ctx := context.Background()
+	m := newManager(t)
+	parent := t.TempDir()
+	gitRepoWithCommitNoOrigin(t, filepath.Join(parent, "api"))
+
+	_, err := m.Add(ctx, project.AddInput{Path: parent, ProjectID: ptr("ws"), AsWorkspace: true})
+	wantCode(t, err, "WORKSPACE_CHILD_ORIGIN_REQUIRED")
+}
+
 // TestManager_AddWorkspaceAdoptsExistingParent verifies that when the parent is
 // already a git repo, Add commits only .gitignore changes, preserves the prior
 // commit history, and registers the children.
diff --git a/backend/internal/service/project/workspace_registration.go b/backend/internal/service/project/workspace_registration.go
index fe072984c..7f5616e9a 100644
--- a/backend/internal/service/project/workspace_registration.go
+++ b/backend/internal/service/project/workspace_registration.go
@@ -213,6 +213,12 @@ func validateWorkspaceChild(ctx context.Context, child string) error {
 			"suggestedFix": "Check out the repository's default branch (for example `main`) and retry.",
 		})
 	}
+	if origin := resolveGitOriginURL(child); origin == "" {
+		return apierr.Invalid("WORKSPACE_CHILD_ORIGIN_REQUIRED", "Workspace child repositories must have an origin remote configured", map[string]any{
+			"path":         child,
+			"suggestedFix": "Run `git remote add origin <url>` in the child repository, then retry.",
+		})
+	}
 	return nil
 }