diff --git a/internal/handler/download_tools.go b/internal/handler/download_tools.go
index a1086f9..1ef3cac 100644
--- a/internal/handler/download_tools.go
+++ b/internal/handler/download_tools.go
@@ -13,6 +13,7 @@ import (
 	"time"
 
 	"github.com/gofiber/fiber/v3"
+	"github.com/sirupsen/logrus"
 
 	"github.com/peterqiu0516/sub-store/internal/middleware"
 	"github.com/peterqiu0516/sub-store/internal/model"
@@ -55,7 +56,8 @@ func (d *Deps) HandleDownloadCollection(c fiber.Ctx) error {
 		ProxyURL:         d.Cfg.Fetcher.ProxyURL,
 	})
 	if err != nil {
-		return failed(c, err.Error(), 500)
+		logrus.WithError(err).Error("Failed to build subscription")
+		return failed(c, "Failed to build subscription", 500)
 	}
 	return d.sendDownloadResponse(c, result, target)
 }
@@ -86,7 +88,8 @@ func (d *Deps) HandleDownloadSource(c fiber.Ctx) error {
 		ProxyURL:         d.Cfg.Fetcher.ProxyURL,
 	})
 	if err != nil {
-		return failed(c, err.Error(), 500)
+		logrus.WithError(err).Error("Failed to build subscription")
+		return failed(c, "Failed to build subscription", 500)
 	}
 	return d.sendDownloadResponse(c, result, target)
 }
diff --git a/internal/handler/handler_test.go b/internal/handler/handler_test.go
index 88c418c..87fa4cf 100644
--- a/internal/handler/handler_test.go
+++ b/internal/handler/handler_test.go
@@ -1836,6 +1836,37 @@ func TestHandleDownloadSourceDisabled(t *testing.T) {
 	assertStatus(t, "DownloadSource disabled", code, 404)
 }
 
+func TestHandleDownloadBuildErrorDoesNotLeakUpstreamURL(t *testing.T) {
+	for _, kind := range []string{"source", "collection"} {
+		t.Run(kind, func(t *testing.T) {
+			server := httptest.NewServer(http.HandlerFunc(func(http.ResponseWriter, *http.Request) {}))
+			upstreamURL := server.URL + "/subscription?token=upstream-secret"
+			server.Close()
+
+			deps := newTestDeps(t)
+			app := newApp(deps)
+			deps.SourceRepo.Upsert(model.SourceRecord{ID: "remote", Name: "Remote", Type: "remote", URL: upstreamURL, Enabled: true})
+
+			path := "/sources/remote/dl-tok?target=json"
+			if kind == "collection" {
+				deps.CollectionRepo.Upsert(model.CollectionRecord{ID: "remote", Name: "Remote", SourceIds: []string{"remote"}, Enabled: true})
+				path = "/collections/remote/dl-tok?target=json"
+			}
+
+			code, body := doRequest(t, app, "GET", path, "", nil)
+			assertStatus(t, kind, code, http.StatusInternalServerError)
+			errorBody, ok := body["error"].(map[string]any)
+			if !ok || errorBody["message"] != "Failed to build subscription" {
+				t.Fatalf("response = %v, want fixed generic error", body)
+			}
+			response, _ := json.Marshal(body)
+			if strings.Contains(string(response), "upstream-secret") || strings.Contains(string(response), upstreamURL) {
+				t.Fatalf("response leaked upstream URL: %s", response)
+			}
+		})
+	}
+}
+
 // ---------------------------------------------------------------------------
 // Preview handlers
 // ---------------------------------------------------------------------------