diff --git a/docs/c-api/mg_net.h/mg_broadcast.md b/docs/c-api/mg_net.h/mg_broadcast.md
index cef0b379..6e966afe 100644
--- a/docs/c-api/mg_net.h/mg_broadcast.md
+++ b/docs/c-api/mg_net.h/mg_broadcast.md
@@ -16,5 +16,5 @@ that can be, and must be, called from a different (non-IO) thread.
 `func` callback function will be called by the IO thread for each
 connection. When called, the event will be `MG_EV_POLL`, and a message will
 be passed as the `ev_data` pointer. Maximum message size is capped
-by `MG_CTL_MSG_MESSAGE_SIZE` which is set to 8192 bytes. 
+by `MG_CTL_MSG_MESSAGE_SIZE` which is set to 8192 bytes by default. 
 
diff --git a/mongoose.c b/mongoose.c
index ffa97c9b..3196c065 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -38,7 +38,9 @@
 /* Amalgamated: #include "mg_http.h" */
 /* Amalgamated: #include "mg_net.h" */
 
+#ifndef MG_CTL_MSG_MESSAGE_SIZE
 #define MG_CTL_MSG_MESSAGE_SIZE 8192
+#endif
 
 /* internals that need to be accessible in unit tests */
 MG_INTERNAL struct mg_connection *mg_do_connect(struct mg_connection *nc,
diff --git a/mongoose.h b/mongoose.h
index 8d9e8f29..2b7c0830 100644
--- a/mongoose.h
+++ b/mongoose.h
@@ -4034,7 +4034,7 @@ int mg_mgr_poll(struct mg_mgr *mgr, int milli);
  * `func` callback function will be called by the IO thread for each
  * connection. When called, the event will be `MG_EV_POLL`, and a message will
  * be passed as the `ev_data` pointer. Maximum message size is capped
- * by `MG_CTL_MSG_MESSAGE_SIZE` which is set to 8192 bytes.
+ * by `MG_CTL_MSG_MESSAGE_SIZE` which is set to 8192 bytes by default.
  */
 void mg_broadcast(struct mg_mgr *mgr, mg_event_handler_t cb, void *data,
                   size_t len);
diff --git a/src/mg_internal.h b/src/mg_internal.h
index 20614234..0e62448e 100644
--- a/src/mg_internal.h
+++ b/src/mg_internal.h
@@ -34,7 +34,9 @@
 #include "mg_http.h"
 #include "mg_net.h"
 
+#ifndef MG_CTL_MSG_MESSAGE_SIZE
 #define MG_CTL_MSG_MESSAGE_SIZE 8192
+#endif
 
 /* internals that need to be accessible in unit tests */
 MG_INTERNAL struct mg_connection *mg_do_connect(struct mg_connection *nc,
diff --git a/src/mg_net.h b/src/mg_net.h
index d854e770..aa8ed171 100644
--- a/src/mg_net.h
+++ b/src/mg_net.h
@@ -225,7 +225,7 @@ int mg_mgr_poll(struct mg_mgr *mgr, int milli);
  * `func` callback function will be called by the IO thread for each
  * connection. When called, the event will be `MG_EV_POLL`, and a message will
  * be passed as the `ev_data` pointer. Maximum message size is capped
- * by `MG_CTL_MSG_MESSAGE_SIZE` which is set to 8192 bytes.
+ * by `MG_CTL_MSG_MESSAGE_SIZE` which is set to 8192 bytes by default.
  */
 void mg_broadcast(struct mg_mgr *mgr, mg_event_handler_t cb, void *data,
                   size_t len);