diff --git a/src/mms/iso_mms/server/mms_server.c b/src/mms/iso_mms/server/mms_server.c
index cfed8824..c387cb8b 100644
--- a/src/mms/iso_mms/server/mms_server.c
+++ b/src/mms/iso_mms/server/mms_server.c
@@ -279,10 +279,11 @@ MmsServer_reserveTransmitBuffer(MmsServer self)
 void
 MmsServer_releaseTransmitBuffer(MmsServer self)
 {
+    self->transmitBuffer->size = 0;
+
 #if (CONFIG_MMS_THREADLESS_STACK != 1)
     Semaphore_post(self->transmitBufferMutex);
 #endif
-    self->transmitBuffer->size = 0;
 }
 
 #if (MMS_OBTAIN_FILE_SERVICE == 1)