diff --git a/DataFormats/Generic/message_list.h b/DataFormats/Generic/message_list.h
index cb5c323c3ee93..068cffa1bee47 100644
--- a/DataFormats/Generic/message_list.h
+++ b/DataFormats/Generic/message_list.h
@@ -56,6 +56,8 @@ class messageList {
     const HdrT* srcHeader = reinterpret_cast<const HdrT*>(headerData);
     // TODO: consistency check
     mDataArray.push_back(messagePair(*srcHeader, payloadMsg));
+
+    return mDataArray.size();
   }
   /** number of data blocks in the list */
   size_t size() {return mDataArray.size();}
diff --git a/DataFormats/Generic/test/testMessageList.cxx b/DataFormats/Generic/test/testMessageList.cxx
index 76dc5e6df4e7b..e187f6b613cab 100644
--- a/DataFormats/Generic/test/testMessageList.cxx
+++ b/DataFormats/Generic/test/testMessageList.cxx
@@ -31,6 +31,8 @@ struct SimpleHeader_t {
 std::ostream& operator<<(std::ostream& stream, SimpleHeader_t header) {
   stream << "Header ID: " << header.id << std::endl;
   stream << "Header Specification: " << std::hex << header.specification;
+
+  return stream;
 }
 
 // more complex message type, some class which wraps around payload
@@ -45,6 +47,8 @@ class TestMsg {
   ~TestMsg() {clear();}
 
   int alloc(int size) {
+    // not yet implemented
+    return 0;
   }
 
   uint8_t* get() const {