diff --git a/doc/sources/tutorial-client.rst b/doc/sources/tutorial-client.rst
index 78c55038..ff998646 100644
--- a/doc/sources/tutorial-client.rst
+++ b/doc/sources/tutorial-client.rst
@@ -260,7 +260,11 @@ data is available to read in the bufferevent input buffer::
         delete_http2_session_data(session_data);
         return;
       }
-      evbuffer_drain(input, readlen);
+      if(evbuffer_drain(input, readlen) != 0) {
+        warnx("Fatal error: evbuffer_drain failed");
+        delete_http2_session_data(session_data);
+        return;
+      }
       if(session_send(session_data) != 0) {
         delete_http2_session_data(session_data);
         return;
diff --git a/doc/sources/tutorial-server.rst b/doc/sources/tutorial-server.rst
index 59705466..4da8a667 100644
--- a/doc/sources/tutorial-server.rst
+++ b/doc/sources/tutorial-server.rst
@@ -296,7 +296,10 @@ functions for these pending data. To process received data, we call
         warnx("Fatal error: %s", nghttp2_strerror((int)readlen));
         return -1;
       }
-      evbuffer_drain(input, readlen);
+      if(evbuffer_drain(input, readlen) != 0) {
+        warnx("Fatal error: evbuffer_drain failed");
+        return -1;
+      }
       if(session_send(session_data) != 0) {
         return -1;
       }