diff --git a/src/socket.h b/src/socket.h
index 3386b7d1d..eba1b89f8 100644
--- a/src/socket.h
+++ b/src/socket.h
@@ -336,23 +336,25 @@ class TCPSocket : public Socket{
    * \param str the string to be sent
    */
   inline void SendStr(const std::string &str) {
-    unsigned len = static_cast<int>(str.length());
+    int len = static_cast<int>(str.length());
     utils::Assert(this->SendAll(&len, sizeof(len)) == sizeof(len),
                   "error during send SendStr");
-    utils::Assert(this->SendAll(str.c_str(), str.length()) == str.length(),
-                  "error during send SendStr");
+    if (len != 0) {
+      utils::Assert(this->SendAll(str.c_str(), str.length()) == str.length(),
+                    "error during send SendStr");
+    }
   }
   /*!
    * \brief recv a string from network
    * \param out_str the string to receive
    */
   inline void RecvStr(std::string *out_str) {
-    unsigned len;
+    int len;
     utils::Assert(this->RecvAll(&len, sizeof(len)) == sizeof(len),
                   "error during send RecvStr");
     out_str->resize(len);
     if (len != 0) {
-      utils::Assert(this->RecvAll(&(*out_str)[0], len) == len,
+      utils::Assert(this->RecvAll(&(*out_str)[0], len) == out_str->length(),
                     "error during send SendStr");
     }
   }