diff --git a/server/get_header.go b/server/get_header.go
index 5e89788c..dc168b32 100644
--- a/server/get_header.go
+++ b/server/get_header.go
@@ -62,7 +62,15 @@ func (m *BoostService) getHeader(log *logrus.Entry, slot phase0.Slot, pubkey, pa
 
 	// Log how late into the slot the request starts
 	slotStartTimestamp := m.genesisTime + uint64(slot)*config.SlotTimeSec
-	msIntoSlot := uint64(time.Now().UTC().UnixMilli()) - slotStartTimestamp*1000
+	// The request can arrive before the slot start (e.g. scheduling jitter
+	// between VC and BN), which would underflow the unsigned subtraction and
+	// trip the late-in-slot guard below. Clamp negative values to zero, i.e.
+	// treat an early request as arriving exactly at slot start.
+	msIntoSlotSigned := time.Now().UTC().UnixMilli() - int64(slotStartTimestamp*1000)
+	var msIntoSlot uint64
+	if msIntoSlotSigned > 0 {
+		msIntoSlot = uint64(msIntoSlotSigned)
+	}
 	log.WithFields(logrus.Fields{
 		"genesisTime": m.genesisTime,
 		"slotTimeSec": config.SlotTimeSec,
diff --git a/server/service_test.go b/server/service_test.go
index 5e78893d..4297e98c 100644
--- a/server/service_test.go
+++ b/server/service_test.go
@@ -326,6 +326,22 @@ func TestGetHeader(t *testing.T) {
 		require.Equal(t, 1, backend.relays[0].GetRequestCount(path))
 	})
 
+	t.Run("Request arriving before slot start still queries relays", func(t *testing.T) {
+		header := make(http.Header)
+		header.Set(HeaderAccept, MediaTypeJSON)
+
+		backend := newTestBackend(t, 1, time.Second)
+		// setting genesisTime so slot 1 starts several seconds in the future,
+		// making msIntoSlot reliably negative regardless of the Unix()
+		// second-truncation. Without clamping, the unsigned subtraction wraps
+		// and the late-in-slot guard skips all relays.
+		backend.boost.genesisTime = uint64(time.Now().Unix()) - 7
+
+		rr := backend.request(t, http.MethodGet, path, header, nil)
+		require.Equal(t, http.StatusOK, rr.Code, rr.Body.String())
+		require.Equal(t, 1, backend.relays[0].GetRequestCount(path))
+	})
+
 	t.Run("Okay response from relay deneb", func(t *testing.T) {
 		header := make(http.Header)
 		header.Set(HeaderAccept, MediaTypeJSON)