diff --git a/fairmq/FairMQChannel.cxx b/fairmq/FairMQChannel.cxx
index eedfd5d1..40f884fe 100644
--- a/fairmq/FairMQChannel.cxx
+++ b/fairmq/FairMQChannel.cxx
@@ -451,12 +451,12 @@ int FairMQChannel::Send(const unique_ptr<FairMQMessage>& msg) const
     return -2;
 }
 
-uint64_t FairMQChannel::Send(const std::vector<std::unique_ptr<FairMQMessage>>& msgVec) const
+int64_t FairMQChannel::Send(const std::vector<std::unique_ptr<FairMQMessage>>& msgVec) const
 {
     // Sending vector typicaly handles more then one part
     if (msgVec.size() > 1)
     {
-        uint64_t totalSize = 0;
+        int64_t totalSize = 0;
 
         for (unsigned int i = 0; i < msgVec.size() - 1; ++i)
         {
@@ -494,7 +494,7 @@ uint64_t FairMQChannel::Send(const std::vector<std::unique_ptr<FairMQMessage>>&
     }
 }
 
-uint64_t FairMQChannel::Receive(std::vector<std::unique_ptr<FairMQMessage>>& msgVec) const
+int64_t FairMQChannel::Receive(std::vector<std::unique_ptr<FairMQMessage>>& msgVec) const
 {
     // Warn if the vector is filled before Receive() and empty it.
     if (msgVec.size() > 0)
@@ -503,7 +503,7 @@ uint64_t FairMQChannel::Receive(std::vector<std::unique_ptr<FairMQMessage>>& msg
         msgVec.clear();
     }
 
-    uint64_t totalSize = 0;
+    int64_t totalSize = 0;
 
     do
     {
diff --git a/fairmq/FairMQChannel.h b/fairmq/FairMQChannel.h
index bf167343..f32b7442 100644
--- a/fairmq/FairMQChannel.h
+++ b/fairmq/FairMQChannel.h
@@ -170,14 +170,14 @@ class FairMQChannel
     /// @param chan channel name
     /// @param i channel index
     /// @return Number of bytes that have been queued. -2 If queueing was not possible or timed out. In case of errors, returns -1.
-    uint64_t Send(const std::vector<std::unique_ptr<FairMQMessage>>& msgVec) const;
+    int64_t Send(const std::vector<std::unique_ptr<FairMQMessage>>& msgVec) const;
 
     /// Shorthand method to receive a vector of messages on `chan` at index `i`
     /// @param msgVec message vector reference
     /// @param chan channel name
     /// @param i channel index
     /// @return Number of bytes that have been received. -2 If reading from the queue was not possible or timed out. In case of errors, returns -1.
-    uint64_t Receive(std::vector<std::unique_ptr<FairMQMessage>>& msgVec) const;
+    int64_t Receive(std::vector<std::unique_ptr<FairMQMessage>>& msgVec) const;
 
     // DEPRECATED socket method wrappers with raw pointers and flag checks
     int Send(FairMQMessage* msg, const std::string& flag = "") const;