diff --git a/a8/fifobuffer.cc b/a8/fifobuffer.cc
index 3b98177..bb48349 100644
--- a/a8/fifobuffer.cc
+++ b/a8/fifobuffer.cc
@@ -17,6 +17,7 @@ namespace a8
         }
         buf_ = (char*)malloc(buf_len);
         buf_len_ = buf_len;
+        capacity_ = buf_len;
     }
 
     FifoBuffer::~FifoBuffer()
@@ -40,7 +41,11 @@ namespace a8
             if (p != buf_ + head_) {
                 abort();
             }
-
+            BufHead* buf_head = (BufHead*)(p - sizeof(BufHead));
+            head_ += sizeof(BufHead) + buf_head->len;
+            if (head_ >= buf_len_) {
+                head_ = 0;
+            }
         } else {
             free(p);
         }
diff --git a/a8/fifobuffer.h b/a8/fifobuffer.h
index 1b081ba..324ff84 100644
--- a/a8/fifobuffer.h
+++ b/a8/fifobuffer.h
@@ -21,6 +21,7 @@ namespace a8
         unsigned int buf_len_ = 0;
         std::atomic<unsigned int> head_ = 0;
         std::atomic<unsigned int> tail_ = 0;
+        std::atomic<unsigned int> capacity_ = 0;
 
     };