diff --git a/README.md b/README.md
index 672c649..2c0b85e 100644
--- a/README.md
+++ b/README.md
@@ -13,7 +13,7 @@ a WebSocket Server and Client for Arduino based on RFC6455.
  - continuation frame
 
 ##### Limitations #####
- - max input length is limited to the ram size and the ```WEBSOCKETS_MAX_DATA_SIZE``` define
+ - max input length is limited to the ram size and the ```WEBSOCKETS_MAX_DATA_SIZE``` define (override it with a build flag, e.g. ```-DWEBSOCKETS_MAX_DATA_SIZE=32768```)
  - max output length has no limit (the hardware is the limit)
  - Client send big frames with mask 0x00000000 (on AVR all frames)
  - continuation frame reassembly need to be handled in the application code
diff --git a/src/WebSockets.h b/src/WebSockets.h
index 8fd7521..68b6aea 100644
--- a/src/WebSockets.h
+++ b/src/WebSockets.h
@@ -63,7 +63,9 @@
 
 #if defined(ESP8266) || defined(ESP32)
 
+#ifndef WEBSOCKETS_MAX_DATA_SIZE
 #define WEBSOCKETS_MAX_DATA_SIZE (15 * 1024)
+#endif
 #define WEBSOCKETS_USE_BIG_MEM
 #define GET_FREE_HEAP ESP.getFreeHeap()
 // moves all Header strings to Flash (~300 Byte)
@@ -79,7 +81,9 @@
 
 #elif defined(STM32_DEVICE)
 
+#ifndef WEBSOCKETS_MAX_DATA_SIZE
 #define WEBSOCKETS_MAX_DATA_SIZE (15 * 1024)
+#endif
 #define WEBSOCKETS_USE_BIG_MEM
 #define GET_FREE_HEAP System.freeMemory()
 #define WEBSOCKETS_YIELD()
@@ -87,7 +91,9 @@
 
 #elif defined(ARDUINO_ARCH_RP2040)
 
+#ifndef WEBSOCKETS_MAX_DATA_SIZE
 #define WEBSOCKETS_MAX_DATA_SIZE (15 * 1024)
+#endif
 #define WEBSOCKETS_USE_BIG_MEM
 #define GET_FREE_HEAP rp2040.getFreeHeap()
 #define WEBSOCKETS_YIELD() yield()
@@ -95,26 +101,34 @@
 
 #elif defined(ARDUINO_UNOWIFIR4)
 
+#ifndef WEBSOCKETS_MAX_DATA_SIZE
 #define WEBSOCKETS_MAX_DATA_SIZE (15 * 1024)
+#endif
 #define WEBSOCKETS_YIELD() yield()
 #define WEBSOCKETS_YIELD_MORE() delay(1)
 
 #elif defined(ARDUINO_SAMD_MKRWIFI1010) || defined(ARDUINO_SAMD_NANO_33_IOT)
 
+#ifndef WEBSOCKETS_MAX_DATA_SIZE
 #define WEBSOCKETS_MAX_DATA_SIZE (15 * 1024)
+#endif
 #define WEBSOCKETS_YIELD() yield()
 #define WEBSOCKETS_YIELD_MORE() delay(1)
 
 #elif defined(WIO_TERMINAL) || defined(SEEED_XIAO_M0)
 
+#ifndef WEBSOCKETS_MAX_DATA_SIZE
 #define WEBSOCKETS_MAX_DATA_SIZE (15 * 1024)
+#endif
 #define WEBSOCKETS_YIELD() yield()
 #define WEBSOCKETS_YIELD_MORE() delay(1)
 
 #else
 
 // atmega328p has only 2KB ram!
+#ifndef WEBSOCKETS_MAX_DATA_SIZE
 #define WEBSOCKETS_MAX_DATA_SIZE (1024)
+#endif
 // moves all Header strings to Flash
 #define WEBSOCKETS_SAVE_RAM
 #define WEBSOCKETS_YIELD()