diff --git a/media/base/audio_block_fifo.cc b/media/base/audio_block_fifo.cc
index d98c40969f9c3..0e5627102189c 100644
--- a/media/base/audio_block_fifo.cc
+++ b/media/base/audio_block_fifo.cc
@@ -82,8 +82,15 @@ void AudioBlockFifo::IncreaseCapacity(int blocks) {
               audio_blocks_.begin() + original_size, audio_blocks_.end());
 
   // Update the write pointer if it is on top of the new inserted blocks.
-  if (write_block_ >= read_block_)
+  // When write_block_ == read_block_ the ring is either empty
+  // (available_blocks_ == 0) or full (available_blocks_ == original_size). In
+  // the full case write_block_ must stay pointing at the first newly-inserted
+  // (empty) slot, otherwise subsequent Push() overwrites unconsumed data and
+  // Consume() returns the never-written AlignedUninit blocks.
+  if (write_block_ > read_block_ ||
+      (write_block_ == read_block_ && available_blocks_ == 0)) {
     write_block_ += blocks;
+  }
 
   // Update the read pointers correspondingly.
   read_block_ += blocks;