diff --git a/mmcutils/mmcutils.c b/mmcutils/mmcutils.c
index f9c7b702a..85516192c 100644
--- a/mmcutils/mmcutils.c
+++ b/mmcutils/mmcutils.c
@@ -439,7 +439,7 @@ mmc_raw_copy (const MmcPartition *partition, char *in_file) {
         goto ERROR2;
 
     fseek(in, 0L, SEEK_END);
-    sz = ftell(in);
+    sz = 1048576*20;//MTK 20MB
     fseek(in, 0L, SEEK_SET);
 
     if (sz % 512)
@@ -490,7 +490,7 @@ mmc_raw_dump_internal (const char* in_file, const char *out_file) {
         goto ERROR2;
 
     fseek(in, 0L, SEEK_END);
-    sz = ftell(in);
+    sz = 1048576*20;//MTK 20MB
     fseek(in, 0L, SEEK_SET);
 
     if (sz % 512)