diff --git a/CHANGELOG.md b/CHANGELOG.md
index 31e8f718..86e6a460 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 Version XXX:
 
+* Fix file open with append_existing flag on posix.
 * Websocket SSL `teardown` also tears down underlying TCP.
 * Update WebSocket examples to set TLS SNI.
 * Add handler tracking locations to websocket.
diff --git a/include/boost/beast/core/impl/file_posix.ipp b/include/boost/beast/core/impl/file_posix.ipp
index 0f7f42ac..61a33a52 100644
--- a/include/boost/beast/core/impl/file_posix.ipp
+++ b/include/boost/beast/core/impl/file_posix.ipp
@@ -172,7 +172,7 @@ open(char const* path, file_mode mode, error_code& ec)
         break;
 
     case file_mode::append_existing:
-        f = O_WRONLY;
+        f = O_WRONLY | O_APPEND;
     #if BOOST_BEAST_USE_POSIX_FADVISE
         advise = POSIX_FADV_SEQUENTIAL;
     #endif