diff --git a/README.md b/README.md
index 527c0e86f..f28abfd31 100755
--- a/README.md
+++ b/README.md
@@ -344,6 +344,7 @@ Remark:
 
 ### SRS 2.0 history
 
+* v2.0, 2015-06-10, fix [#424](https://github.com/simple-rtmp-server/srs/issues/424) fix aggregate timestamp bug. 2.0.174
 * v2.0, 2015-06-06, fix [#421](https://github.com/simple-rtmp-server/srs/issues/421) drop video for unkown RTMP header.
 * v2.0, 2015-06-05, fix [#420](https://github.com/simple-rtmp-server/srs/issues/420) remove ts for hls ram mode.
 * v2.0, 2015-05-30, fix [#209](https://github.com/simple-rtmp-server/srs/issues/209) cleanup hls when stop and timeout. 2.0.173.
diff --git a/trunk/src/app/srs_app_source.cpp b/trunk/src/app/srs_app_source.cpp
index b30bf9c3f..343056522 100755
--- a/trunk/src/app/srs_app_source.cpp
+++ b/trunk/src/app/srs_app_source.cpp
@@ -1922,7 +1922,8 @@ int SrsSource::on_aggregate(SrsCommonMessage* msg)
         timestamp &= 0x7FFFFFFF;
         
         // adjust abs timestamp in aggregate msg.
-        if (delta < 0) {
+        // only -1 means uninitialized delta.
+        if (delta == -1) {
             delta = (int)msg->header.timestamp - (int)timestamp;
         }
         timestamp += delta;
diff --git a/trunk/src/core/srs_core.hpp b/trunk/src/core/srs_core.hpp
index cb1e34055..3985cdcd7 100644
--- a/trunk/src/core/srs_core.hpp
+++ b/trunk/src/core/srs_core.hpp
@@ -31,7 +31,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 // current release version
 #define VERSION_MAJOR       2
 #define VERSION_MINOR       0
-#define VERSION_REVISION    173
+#define VERSION_REVISION    174
 
 // server info.
 #define RTMP_SIG_SRS_KEY "SRS"