diff --git a/src/mem/ruby/network/MessageBuffer.cc b/src/mem/ruby/network/MessageBuffer.cc
index 557e0e80e..b96b00504 100644
--- a/src/mem/ruby/network/MessageBuffer.cc
+++ b/src/mem/ruby/network/MessageBuffer.cc
@@ -40,7 +40,7 @@ using namespace std;
 using m5::stl_helpers::operator<<;
 
 MessageBuffer::MessageBuffer(const Params *p)
-    : SimObject(p),
+    : SimObject(p), m_stall_map_size(0),
     m_max_size(p->buffer_size), m_time_last_time_size_checked(0),
     m_time_last_time_enqueue(0), m_time_last_time_pop(0),
     m_last_arrival_time(0), m_strict_fifo(p->ordered),
@@ -99,7 +99,7 @@ MessageBuffer::areNSlotsAvailable(unsigned int n, Tick current_time)
     }
 
     // now compare the new size with our max size
-    if (current_size + n <= m_max_size) {
+    if (current_size + m_stall_map_size + n <= m_max_size) {
         return true;
     } else {
         DPRINTF(RubyQueue, "n: %d, current_size: %d, heap size: %d, "
@@ -289,6 +289,8 @@ MessageBuffer::reanalyzeMessages(Addr addr, Tick current_time)
     // scheduled for the current cycle so that the previously stalled messages
     // will be observed before any younger messages that may arrive this cycle
     //
+    m_stall_map_size -= m_stall_msg_map[addr].size();
+    assert(m_stall_map_size >= 0);
     reanalyzeList(m_stall_msg_map[addr], current_time);
     m_stall_msg_map.erase(addr);
 }
@@ -306,6 +308,8 @@ MessageBuffer::reanalyzeAllMessages(Tick current_time)
     //
     for (StallMsgMapType::iterator map_iter = m_stall_msg_map.begin();
          map_iter != m_stall_msg_map.end(); ++map_iter) {
+        m_stall_map_size -= map_iter->second.size();
+        assert(m_stall_map_size >= 0);
         reanalyzeList(map_iter->second, current_time);
     }
     m_stall_msg_map.clear();
@@ -327,6 +331,7 @@ MessageBuffer::stallMessage(Addr addr, Tick current_time)
     // these addresses change state.
     //
     (m_stall_msg_map[addr]).push_back(message);
+    m_stall_map_size++;
 }
 
 void
diff --git a/src/mem/ruby/network/MessageBuffer.hh b/src/mem/ruby/network/MessageBuffer.hh
index 2a82887cd..b1d04ab9a 100644
--- a/src/mem/ruby/network/MessageBuffer.hh
+++ b/src/mem/ruby/network/MessageBuffer.hh
@@ -137,9 +137,37 @@ class MessageBuffer : public SimObject
     // sorted and ensures a well-defined iteration order
     typedef std::map<Addr, std::list<MsgPtr> > StallMsgMapType;
 
+    /**
+     * A map from line addresses to lists of stalled messages for that line.
+     * If this buffer allows the receiver to stall messages, on a stall
+     * request, the stalled message is removed from the m_prio_heap and placed
+     * in the m_stall_msg_map. Messages are held there until the receiver
+     * requests they be reanalyzed, at which point they are moved back to
+     * m_prio_heap.
+     *
+     * NOTE: The stall map holds messages in the order in which they were
+     * initially received, and when a line is unblocked, the messages are
+     * moved back to the m_prio_heap in the same order. This prevents starving
+     * older requests with younger ones.
+     */
     StallMsgMapType m_stall_msg_map;
 
+    /**
+     * Current size of the stall map.
+     * Track the number of messages held in stall map lists. This is used to
+     * ensure that if the buffer is finite-sized, it blocks further requests
+     * when the m_prio_heap and m_stall_msg_map contain m_max_size messages.
+     */
+    int m_stall_map_size;
+
+    /**
+     * The maximum capacity. For finite-sized buffers, m_max_size stores a
+     * number greater than 0 to indicate the maximum allowed number of messages
+     * in the buffer at any time. To get infinitely-sized buffers, set buffer
+     * size: m_max_size = 0
+     */
     const unsigned int m_max_size;
+
     Tick m_time_last_time_size_checked;
     unsigned int m_size_last_time_size_checked;