diff --git a/media/libstagefright/MPEG4Writer.cpp b/media/libstagefright/MPEG4Writer.cpp
index a0f17b5..42885dd 100644
--- a/media/libstagefright/MPEG4Writer.cpp
+++ b/media/libstagefright/MPEG4Writer.cpp
@@ -43,7 +43,9 @@
 namespace android {
 
 static const int64_t kMinStreamableFileSizeInBytes = 5 * 1024 * 1024;
-static const int64_t kMax32BitFileSize = 0x007fffffffLL;
+static const int64_t kMax32BitFileSize = 0x00ffffffffLL; // 2^32-1 : max FAT32
+                                                         // filesystem file size
+                                                         // used by most SD cards
 static const uint8_t kNalUnitTypeSeqParamSet = 0x07;
 static const uint8_t kNalUnitTypePicParamSet = 0x08;
 static const int64_t kInitialDelayTimeUs     = 700000LL;
@@ -860,11 +862,11 @@
     // Fix up the size of the 'mdat' chunk.
     if (mUse32BitOffset) {
         lseek64(mFd, mMdatOffset, SEEK_SET);
-        int32_t size = htonl(static_cast<int32_t>(mOffset - mMdatOffset));
+        uint32_t size = htonl(static_cast<uint32_t>(mOffset - mMdatOffset));
         ::write(mFd, &size, 4);
     } else {
         lseek64(mFd, mMdatOffset + 8, SEEK_SET);
-        int64_t size = mOffset - mMdatOffset;
+        uint64_t size = mOffset - mMdatOffset;
         size = hton64(size);
         ::write(mFd, &size, 8);
     }