diff --git a/exec/ipc.c b/exec/ipc.c
index 495e4305..977f60c0 100644
--- a/exec/ipc.c
+++ b/exec/ipc.c
@@ -99,7 +99,9 @@ LOGSYS_DECLARE_SUBSYS ("IPC", LOG_INFO);
 /*
  * When there are this many entries left in a queue, turn on flow control
  */
+#ifndef FLOW_CONTROL_ENTRIES_ENABLE
 #define FLOW_CONTROL_ENTRIES_ENABLE 400
+#endif /* FLOW_CONTROL_ENTRIES_ENABLE */
 
 /*
  * When there are this many entries in a queue, turn off flow control
diff --git a/exec/main.h b/exec/main.h
index e9b11d2b..73f964a0 100644
--- a/exec/main.h
+++ b/exec/main.h
@@ -48,7 +48,9 @@
  * Size of the queue (entries) for I/O's to the API over socket IPC.
  */
 
+#ifndef SIZEQUEUE
 #define SIZEQUEUE 800
+#endif /* SIZEQUEUE */
 
 #define SOCKET_SERVICE_INIT 254
 
diff --git a/exec/totemconfig.c b/exec/totemconfig.c
index 146d1e46..a7a59323 100644
--- a/exec/totemconfig.c
+++ b/exec/totemconfig.c
@@ -528,9 +528,9 @@ int totem_config_validate (
 		totem_config->net_mtu = 1500;
 	}
 
-	if ((MESSAGE_SIZE_MAX / totem_config->net_mtu) < totem_config->max_messages) {
+	if ((MESSAGE_QUEUE_MAX) < totem_config->max_messages) {
 		sprintf (local_error_reason, "The max_messages parameter (%d messages) may not be greater then (%d messages).",
-			totem_config->max_messages, MESSAGE_SIZE_MAX / totem_config->net_mtu);
+			totem_config->max_messages, MESSAGE_QUEUE_MAX);
 		goto parse_error;
 	}
 
diff --git a/exec/totemsrp.c b/exec/totemsrp.c
index e42dbfa8..4810bb9b 100644
--- a/exec/totemsrp.c
+++ b/exec/totemsrp.c
@@ -822,7 +822,7 @@ int totemsrp_initialize (
 	 * Must have net_mtu adjusted by totemrrp_initialize first
 	 */
 	queue_init (&instance->new_message_queue,
-		(MESSAGE_SIZE_MAX / (totem_config->net_mtu - 25) /* for totempg_mcat header */),
+		MESSAGE_QUEUE_MAX,
 		sizeof (struct message_item));
 
 	return (0);
diff --git a/include/corosync/engine/coroapi.h b/include/corosync/engine/coroapi.h
index 2d095c98..dc96fdf5 100644
--- a/include/corosync/engine/coroapi.h
+++ b/include/corosync/engine/coroapi.h
@@ -52,7 +52,14 @@ struct corosync_tpg_group {
 
 #define PROCESSOR_COUNT_MAX 384
 #define INTERFACE_MAX 2
-#define MESSAGE_SIZE_MAX        1024*1024 /* (1MB) */
+
+#ifndef MESSAGE_SIZE_MAX
+#define MESSAGE_SIZE_MAX	1024*1024 /* (1MB) */
+#endif /* MESSAGE_SIZE_MAX */
+
+#ifndef MESSAGE_QUEUE_MAX
+#define MESSAGE_QUEUE_MAX MESSAGE_SIZE_MAX / totem_config->net_mtu
+#endif /* MESSAGE_QUEUE_MAX */
 
 #define TOTEM_AGREED	0
 #define TOTEM_SAFE	1
diff --git a/include/corosync/totem/totem.h b/include/corosync/totem/totem.h
index a5a5511f..4a0715a7 100644
--- a/include/corosync/totem/totem.h
+++ b/include/corosync/totem/totem.h
@@ -36,7 +36,14 @@
 #define TOTEM_H_DEFINED
 #include "totemip.h"
 
+#ifndef MESSAGE_SIZE_MAX
 #define MESSAGE_SIZE_MAX	1024*1024 /* (1MB) */
+#endif /* MESSAGE_SIZE_MAX */
+
+#ifndef MESSAGE_QUEUE_MAX
+#define MESSAGE_QUEUE_MAX MESSAGE_SIZE_MAX / totem_config->net_mtu
+#endif /* MESSAGE_QUEUE_MAX */
+
 #define PROCESSOR_COUNT_MAX	384
 #define FRAME_SIZE_MAX		9000
 #define TRANSMITS_ALLOWED	16