diff --git a/src/librfu_rfu.c b/src/librfu_rfu.c
index 20d11352a1..fa8137f408 100644
--- a/src/librfu_rfu.c
+++ b/src/librfu_rfu.c
@@ -1430,7 +1430,11 @@ static u16 rfu_STC_setSendData_org(u8 ni_or_uni, u8 bmSendSlot, u8 subFrameSize,
     else if (gRfuLinkStatus->parentChild == MODE_CHILD)
         llFrameSize_p = &gRfuLinkStatus->remainLLFrameSizeChild[bm_slot_id];
     frameSize = llsf_struct[gRfuLinkStatus->parentChild].frameSize;
+#if UBFIX
+    if (llFrameSize_p && (subFrameSize > *llFrameSize_p || subFrameSize <= frameSize))
+#else
     if (subFrameSize > *llFrameSize_p || subFrameSize <= frameSize)
+#endif
         return ERR_SUBFRAME_SIZE;
     imeBak = REG_IME;
     REG_IME = 0;
@@ -1468,7 +1472,10 @@ static u16 rfu_STC_setSendData_org(u8 ni_or_uni, u8 bmSendSlot, u8 subFrameSize,
             } while (0);
         }
         gRfuLinkStatus->sendSlotNIFlag |= bmSendSlot;
-        *llFrameSize_p -= subFrameSize;
+#if UBFIX
+        if (llFrameSize_p)
+#endif
+            *llFrameSize_p -= subFrameSize;
         slotStatus_NI->send.state = SLOT_STATE_SEND_START;
     }
     else if (ni_or_uni & 0x10)
@@ -1477,7 +1484,10 @@ static u16 rfu_STC_setSendData_org(u8 ni_or_uni, u8 bmSendSlot, u8 subFrameSize,
         slotStatus_UNI->send.bmSlot = bmSendSlot;
         slotStatus_UNI->send.src = src;
         slotStatus_UNI->send.payloadSize = subFrameSize - frameSize;
-        *llFrameSize_p -= subFrameSize;
+#if UBFIX
+        if (llFrameSize_p)
+#endif
+            *llFrameSize_p -= subFrameSize;
         slotStatus_UNI->send.state = SLOT_STATE_SEND_UNI;
         gRfuLinkStatus->sendSlotUNIFlag |= bmSendSlot;
     }