diff --git a/packager/media/file/io_cache.cc b/packager/media/file/io_cache.cc
index 136ba09080..3e04aaa4db 100644
--- a/packager/media/file/io_cache.cc
+++ b/packager/media/file/io_cache.cc
@@ -35,7 +35,7 @@ IoCache::~IoCache() {
   Close();
 }
 
-int64_t IoCache::Read(void* buffer, uint64_t size) {
+uint64_t IoCache::Read(void* buffer, uint64_t size) {
   DCHECK(buffer);
 
   AutoLock lock(lock_);
@@ -65,7 +65,7 @@ int64_t IoCache::Read(void* buffer, uint64_t size) {
   return size;
 }
 
-int64_t IoCache::Write(const void* buffer, uint64_t size) {
+uint64_t IoCache::Write(const void* buffer, uint64_t size) {
   DCHECK(buffer);
 
   const uint8_t* r_ptr(static_cast<const uint8_t*>(buffer));
diff --git a/packager/media/file/io_cache.h b/packager/media/file/io_cache.h
index b6cc6ae9c5..fb898aef4e 100644
--- a/packager/media/file/io_cache.h
+++ b/packager/media/file/io_cache.h
@@ -28,7 +28,7 @@ class IoCache {
   /// @param size is the size of @a buffer.
   /// @return the number of bytes read into @a buffer, or 0 if the call
   ///         unblocked because the cache has been closed.
-  int64_t Read(void* buffer, uint64_t size);
+  uint64_t Read(void* buffer, uint64_t size);
 
   /// Write data to the cache. This function may block until there is enough
   /// room in the cache.
@@ -37,7 +37,7 @@ class IoCache {
   /// @return the amount of data written to the buffer (which will equal
   ///         @a data), or 0 if the call unblocked because the cache has been
   ///         closed.
-  int64_t Write(const void* buffer, uint64_t size);
+  uint64_t Write(const void* buffer, uint64_t size);
 
   /// Empties the cache.
   void Clear();
diff --git a/packager/media/file/io_cache_unittest.cc b/packager/media/file/io_cache_unittest.cc
index a377775d21..d3fbeeae50 100644
--- a/packager/media/file/io_cache_unittest.cc
+++ b/packager/media/file/io_cache_unittest.cc
@@ -147,7 +147,7 @@ TEST_F(IoCacheTest, LotsOfUnalignedBlocks) {
   while (verify_index < verify_buffer.size()) {
     std::vector<uint8_t> read_buffer2(kBlockSize);
     uint64_t bytes_read = cache_->Read(&read_buffer2[0], kBlockSize);
-    EXPECT_NE(0, bytes_read);
+    EXPECT_NE(0U, bytes_read);
     EXPECT_FALSE(memcmp(&verify_buffer[verify_index],
                         &read_buffer2[0],
                         bytes_read));
@@ -204,7 +204,7 @@ TEST_F(IoCacheTest, CloseByWriter) {
   uint8_t test_buffer[kBlockSize];
   std::vector<uint8_t> write_buffer;
   WriteToCacheThreaded(write_buffer, 0, 0, true);
-  EXPECT_EQ(0, cache_->Read(test_buffer, kBlockSize));
+  EXPECT_EQ(0U, cache_->Read(test_buffer, kBlockSize));
   WaitForWriterThread();
 }