diff --git a/src/msg.cpp b/src/msg.cpp
index 2fc2274f..f83ca056 100644
--- a/src/msg.cpp
+++ b/src/msg.cpp
@@ -58,7 +58,7 @@ int zmq::msg_t::init_size (size_t size_)
         u.lmsg.flags = 0;
         u.lmsg.content =
             (content_t*) malloc (sizeof (content_t) + size_);
-        if (!u.lmsg.content) {
+        if (unlikely (!u.lmsg.content)) {
             errno = ENOMEM;
             return -1;
         }
@@ -75,7 +75,11 @@ int zmq::msg_t::init_size (size_t size_)
 int zmq::msg_t::init_data (void *data_, size_t size_, msg_free_fn *ffn_,
     void *hint_)
 {
-    // Initialize constant message if there's no need to deallocate
+    //  If data is NULL and size is not 0, a segfault
+    //  would occur once the data is accessed
+    assert (data_ != NULL || size_ == 0);
+    
+    //  Initialize constant message if there's no need to deallocate
     if(ffn_ == NULL) {
         u.cmsg.type = type_cmsg;
         u.cmsg.flags = 0;
diff --git a/src/msg.hpp b/src/msg.hpp
index bc0a9376..bac1f09a 100644
--- a/src/msg.hpp
+++ b/src/msg.hpp
@@ -44,7 +44,7 @@ namespace zmq
     {
     public:
 
-        //  Mesage flags.
+        //  Message flags.
         enum
         {
             more = 1,
@@ -105,10 +105,13 @@ namespace zmq
         enum type_t
         {
             type_min = 101,
+            //  VSM messages store the content in the message itself
             type_vsm = 101,
+            //  LMSG messages store the content in malloc-ed memory
             type_lmsg = 102,
+            //  Delimiter messages are used in envelopes
             type_delimiter = 103,
-            // CMSG messages point to constant data
+            //  CMSG messages point to constant data
             type_cmsg = 104,
             type_max = 104
         };
diff --git a/src/zmq.cpp b/src/zmq.cpp
index def0ba91..ff3e60fa 100644
--- a/src/zmq.cpp
+++ b/src/zmq.cpp
@@ -539,7 +539,7 @@ int zmq_recviov (void *s_, iovec *a_, size_t *count_, int flags_)
 
         a_[i].iov_len = zmq_msg_size (&msg);
         a_[i].iov_base = malloc(a_[i].iov_len);
-        if (!a_[i].iov_base) {
+        if (unlikely (!a_[i].iov_base)) {
             errno = ENOMEM;
             return -1;
         }