diff --git a/include/librfu.h b/include/librfu.h
index aff96a72ce..69c6961729 100644
--- a/include/librfu.h
+++ b/include/librfu.h
@@ -371,8 +371,7 @@ struct NIComm
     u16 state;                     // Communication state of slot
     u16 failCounter;               // Count of failed transmissions/receptions (Count is increased when transmission/reception of data does not succeed within 1PF=16.7 ms)
     const u8 *now_p[WINDOW_COUNT]; // Address of current send/receive (The data is divided into WINDOW_COUNT blocks and sent in payloadSize units.)
-    // remainSize is u32 in SDK. This is a hack to match ASM
-    s32 remainSize;                // Size of remaining communication data
+    u32 remainSize;                // Size of remaining communication data
     u16 errorCode;                 // Error code
     u8 bmSlot;                     // Expresses the current communication slot in bits
                                    //   (When sending from the Master, because multiple slaves can be specified with bmSlot, communications are terminated based on the failCounter for each child device)
diff --git a/src/librfu_rfu.c b/src/librfu_rfu.c
index 061dc76ad1..3f5bd8b694 100644
--- a/src/librfu_rfu.c
+++ b/src/librfu_rfu.c
@@ -1,3 +1,4 @@
+#include <limits.h>
 #include "librfu.h"
 
 struct LLSFStruct
@@ -1797,7 +1798,7 @@ static u16 rfu_STC_NI_constructLLSF(u8 bm_slot_id, u8 **dest_pp, struct NIComm *
     }
     else
     {
-        if ((u32)NI_comm->remainSize >= NI_comm->payloadSize)
+        if (NI_comm->remainSize >= NI_comm->payloadSize)
             size = NI_comm->payloadSize;
         else
             size = NI_comm->remainSize;
@@ -2092,34 +2093,31 @@ static void rfu_STC_NI_receive_Sender(u8 NI_slot, u8 bm_flag, const struct RfuLo
             else
                 NI_comm->now_p[llsf_NI->phase] += NI_comm->payloadSize << 2;
             NI_comm->remainSize -= NI_comm->payloadSize;
-            if (NI_comm->remainSize != 0)
-                if (NI_comm->remainSize >= 0)
-                    goto _081E30AE;
-            // Above is a hack to avoid optimization over comparison.
-            // rfu_STC_NI_constructLLSF uses this field as u32.
-            // It's equivalent to the following condition:
-            // if (NI_comm->remainSize == 0 || NI_comm->remainSize < 0)
+            switch (NI_comm->remainSize)
+            {
+            default:
+            case 0:
+                NI_comm->phase = 0;
+                if (NI_comm->state == SLOT_STATE_SEND_START)
                 {
-                    NI_comm->phase = 0;
-                    if (NI_comm->state == SLOT_STATE_SEND_START)
+                    for (i = 0; i < WINDOW_COUNT; ++i)
                     {
-                        for (i = 0; i < WINDOW_COUNT; ++i)
-                        {
-                            NI_comm->n[i] = 1;
-                            NI_comm->now_p[i] = NI_comm->src + NI_comm->payloadSize * i;
-                        }
-                        NI_comm->remainSize = NI_comm->dataSize;
-                        NI_comm->state = SLOT_STATE_SENDING;
-                    }
-                    else
-                    {
-                        NI_comm->n[0] = 0;
-                        NI_comm->remainSize = 0;
-                        NI_comm->state = SLOT_STATE_SEND_LAST;
+                        NI_comm->n[i] = 1;
+                        NI_comm->now_p[i] = NI_comm->src + NI_comm->payloadSize * i;
                     }
+                    NI_comm->remainSize = NI_comm->dataSize;
+                    NI_comm->state = SLOT_STATE_SENDING;
                 }
-        _081E30AE:
-            ;
+                else
+                {
+                    NI_comm->n[0] = 0;
+                    NI_comm->remainSize = 0;
+                    NI_comm->state = SLOT_STATE_SEND_LAST;
+                }
+                break;
+            case 1 ... INT_MAX:
+                break;
+            }
         }
         else if (NI_comm->state == SLOT_STATE_SEND_LAST)
         {