diff --git a/backend/internal/handler/auth_handler.go b/backend/internal/handler/auth_handler.go
index a9379f0a..8bee99d9 100644
--- a/backend/internal/handler/auth_handler.go
+++ b/backend/internal/handler/auth_handler.go
@@ -718,9 +718,13 @@ func (h *AuthHandler) Signup(c *fiber.Ctx) error {
 	slog.Info("[Signup] Forcing AffiliationType to GENERAL (Default personal tenant signup policy)", "email", req.Email)
 
 	var tenantID *string
-	tenant, err := createPersonalTenantForUser(c.Context(), h.TenantService, req.Email)
-	if err != nil {
-		return errorJSON(c, fiber.StatusServiceUnavailable, "failed to create personal tenant")
+	tenant, err := h.TenantService.GetTenantBySlug(c.Context(), "personal")
+	if err != nil || tenant == nil {
+		// Fallback: 만약 시드된 personal 테넌트가 없을 경우 개인별 테넌트를 자동 생성합니다.
+		tenant, err = createPersonalTenantForUser(c.Context(), h.TenantService, req.Email)
+		if err != nil {
+			return errorJSON(c, fiber.StatusServiceUnavailable, "failed to resolve personal tenant")
+		}
 	}
 	tenantID = &tenant.ID
 
diff --git a/backend/internal/handler/auth_handler_signup_test.go b/backend/internal/handler/auth_handler_signup_test.go
index 2fdd4ea9..7d1e479e 100644
--- a/backend/internal/handler/auth_handler_signup_test.go
+++ b/backend/internal/handler/auth_handler_signup_test.go
@@ -127,6 +127,7 @@ func TestSignup_TenantSlugValidation(t *testing.T) {
 		body, _ := json.Marshal(reqBody)
 
 		validTenant := &domain.Tenant{ID: "personal-t1", Slug: "personal-slug", Status: domain.TenantStatusActive}
+		mockTenantSvc.On("GetTenantBySlug", mock.Anything, "personal").Return((*domain.Tenant)(nil), assert.AnError).Once()
 		mockTenantSvc.On("RegisterTenant", mock.Anything, "Personal - user@hanmaceng.co.kr", mock.Anything, domain.TenantTypePersonal, "Automatically provisioned personal tenant", []string(nil), (*string)(nil), "").Return(validTenant, nil).Once()
 		mockIdp.On("CreateUser", mock.Anything, mock.Anything).Return("user-id", nil).Once()
 		mockRedis.On("Delete", mock.Anything).Return(nil)