diff --git a/spindle/hydrant.go b/spindle/hydrant.go
index d669c16cf..027aa454e 100644
--- a/spindle/hydrant.go
+++ b/spindle/hydrant.go
@@ -267,7 +267,7 @@ func (b *backfill) cursorPath() string {
 }
 
 func (b *backfill) settings() map[string]string {
-	return map[string]string{
+	settings := map[string]string{
 		"HYDRANT_DATABASE_PATH":      filepath.Join(b.dir, "db"),
 		"HYDRANT_API_BIND":           "unix:" + b.socketPath(),
 		"HYDRANT_PLC_URL":            b.s.cfg.Server.PlcUrl,
@@ -281,6 +281,11 @@ func (b *backfill) settings() map[string]string {
 		"HYDRANT_IDENTITY_CACHE_SIZE": "50000",
 		"RUST_LOG":                    "warn",
 	}
+	// dev hosts resolve to loopback, so hydrant needs the private network flag
+	if b.s.cfg.Server.Dev {
+		settings["HYDRANT_ALLOW_PRIVATE_NETWORKS"] = "true"
+	}
+	return settings
 }
 
 // round starts hydrant, hands it the queued owners and due retries, and
diff --git a/spindle/hydrant_test.go b/spindle/hydrant_test.go
index 34865fffb..73f3b02b7 100644
--- a/spindle/hydrant_test.go
+++ b/spindle/hydrant_test.go
@@ -871,6 +871,18 @@ func TestBackfillRequeuesOwnersWhenHydrantFailsToStart(t *testing.T) {
 	}
 }
 
+func TestBackfillSettingsAllowPrivateNetworksOnlyInDev(t *testing.T) {
+	for _, dev := range []bool{false, true} {
+		cfg := &config.Config{}
+		cfg.Server.Dev = dev
+		b := newBackfill(&Spindle{cfg: cfg}, slog.Default(), shortTempDir(t))
+		got, ok := b.settings()["HYDRANT_ALLOW_PRIVATE_NETWORKS"]
+		if ok != dev || (dev && got != "true") {
+			t.Errorf("dev=%v: HYDRANT_ALLOW_PRIVATE_NETWORKS = %q (set: %v)", dev, got, ok)
+		}
+	}
+}
+
 // real hydrant, offline. nothing resolves so nothing backfills, but it has to
 // start, answer, shut down and let go of its db for the next round
 func TestBackfillRunsEmbeddedHydrant(t *testing.T) {