diff --git a/a8/fifobuffer.cc b/a8/fifobuffer.cc
index 1a6a9dc..3b98177 100644
--- a/a8/fifobuffer.cc
+++ b/a8/fifobuffer.cc
@@ -2,6 +2,11 @@
 
 #include <a8/fifobuffer.h>
 
+struct BufHead
+{
+    int len = 0;
+};
+
 namespace a8
 {
 
@@ -26,12 +31,19 @@ namespace a8
         if (len <= 0) {
             abort();
         }
-        unsigned int real_len = len + 4;
+        unsigned int real_len = len + sizeof(BufHead);
     }
 
     void FifoBuffer::Free(char* p)
     {
+        if (p >= buf_ && p < buf_ + buf_len_) {
+            if (p != buf_ + head_) {
+                abort();
+            }
 
+        } else {
+            free(p);
+        }
     }
 
 }
diff --git a/a8/fifobuffer.h b/a8/fifobuffer.h
index ee0fb49..1b081ba 100644
--- a/a8/fifobuffer.h
+++ b/a8/fifobuffer.h
@@ -19,8 +19,8 @@ namespace a8
 
         char* buf_ = nullptr;
         unsigned int buf_len_ = 0;
-        std::atomic<unsigned int> start_ = 0;
-        std::atomic<unsigned int> end_ = 0;
+        std::atomic<unsigned int> head_ = 0;
+        std::atomic<unsigned int> tail_ = 0;
 
     };