diff --git a/media/libstagefright/codecs/aacenc/src/bitbuffer.c b/media/libstagefright/codecs/aacenc/src/bitbuffer.c
index a706893..0ce93d3 100644
--- a/media/libstagefright/codecs/aacenc/src/bitbuffer.c
+++ b/media/libstagefright/codecs/aacenc/src/bitbuffer.c
@@ -152,6 +152,7 @@
 
   wBitPos = hBitBuf->wBitPos;
   wBitPos += noBitsToWrite;
+  writeValue &= ~(0xffffffff << noBitsToWrite); // Mask out everything except the lowest noBitsToWrite bits
   writeValue <<= 32 - wBitPos;
   writeValue |= hBitBuf->cache;