diff --git a/src/mms/asn1/ber_decode.c b/src/mms/asn1/ber_decode.c
index 7eca9308..00e82133 100644
--- a/src/mms/asn1/ber_decode.c
+++ b/src/mms/asn1/ber_decode.c
@@ -82,6 +82,43 @@ BerDecoder_decodeUint32(uint8_t* buffer, int intlen, int bufPos) {
     return value;
 }
 
+int32_t
+BerDecoder_decodeInt32(uint8_t* buffer, int intlen, int bufPos) 
+{
+    int32_t value = 0;
+
+    int flag = buffer[bufPos]&0x80;//flag=1表示负数，flag=0表示正数
+
+    int i=0;
+
+    if(flag)
+    {
+        for(i=0;i<4;i++)
+        {
+            value<<=8;
+            if(i<4-intlen)
+            {
+                value+=0xff;
+            }
+            else
+            {
+                value+=buffer[bufPos + i-(4-intlen)];
+            }
+        }
+    }
+    else
+    {
+        for (i = 0; i < intlen; i++) 
+        {
+            value <<= 8;
+            value += buffer[bufPos + i];
+        }
+    }
+    
+    return value;
+}
+
+
 float
 BerDecoder_decodeFloat(uint8_t* buffer, int bufPos)
 {
diff --git a/src/mms/inc_private/ber_decode.h b/src/mms/inc_private/ber_decode.h
index 258f6a21..8bdbcc3e 100644
--- a/src/mms/inc_private/ber_decode.h
+++ b/src/mms/inc_private/ber_decode.h
@@ -34,6 +34,9 @@ BerDecoder_decodeString(uint8_t* buffer, int strlen, int bufPos, int maxBufPos);
 uint32_t
 BerDecoder_decodeUint32(uint8_t* buffer, int intlen, int bufPos);
 
+int32_t
+BerDecoder_decodeInt32(uint8_t* buffer, int intlen, int bufPos);
+
 float
 BerDecoder_decodeFloat(uint8_t* buffer, int bufPos);
 
diff --git a/src/mms/iso_mms/client/mms_client_files.c b/src/mms/iso_mms/client/mms_client_files.c
index a6603ebc..b0e75494 100644
--- a/src/mms/iso_mms/client/mms_client_files.c
+++ b/src/mms/iso_mms/client/mms_client_files.c
@@ -212,7 +212,7 @@ mmsClient_handleFileReadRequest(
     uint32_t invokeId,
     ByteBuffer* response)
 {
-    int32_t frsmId = (int32_t) BerDecoder_decodeUint32(buffer, maxBufPos - bufPos, bufPos);
+    int32_t frsmId = BerDecoder_decodeInt32(buffer, maxBufPos - bufPos, bufPos);
 
     if (DEBUG_MMS_CLIENT)
         printf("MMS_CLIENT: mmsClient_handleFileReadRequest read request for frsmId: %i\n", frsmId);
@@ -232,7 +232,7 @@ mmsClient_handleFileCloseRequest(
     uint32_t invokeId,
     ByteBuffer* response)
 {
-    int32_t frsmId = (int32_t) BerDecoder_decodeUint32(buffer, maxBufPos - bufPos, bufPos);
+    int32_t frsmId = BerDecoder_decodeInt32(buffer, maxBufPos - bufPos, bufPos);
 
     MmsFileReadStateMachine* frsm = getFrsm(connection, frsmId);
 
@@ -698,7 +698,7 @@ mmsMsg_parseFileOpenResponse(uint8_t* buffer, int bufPos, int maxBufPos, int32_t
 
         switch (tag) {
         case 0x80: /* frsmId */
-            *frsmId = (int32_t) BerDecoder_decodeUint32(buffer, length, bufPos);
+            *frsmId = BerDecoder_decodeInt32(buffer, length, bufPos);
 
             bufPos += length;
             break;