diff --git a/src/fader.cpp b/src/fader.cpp
index a867152..6a8ac6c 100644
--- a/src/fader.cpp
+++ b/src/fader.cpp
@@ -10,12 +10,12 @@ struct Colour {
 	int16_t red, green, blue; // value range is 0 to 255
 };
 
-struct Colour curColour[NUM_MODULES];
-struct Colour targetColour[NUM_MODULES];
+struct Colour curColour[MAX_NUM_MODULES];
+struct Colour targetColour[MAX_NUM_MODULES];
 
 void fader_init(void)
 {
-	for(uint32_t i = 0; i < NUM_MODULES; i++) {
+	for(uint32_t i = 0; i < ws2801_num_modules; i++) {
 		curColour[i].red   = targetColour[i].red   = 0;
 		curColour[i].green = targetColour[i].green = 0;
 		curColour[i].blue  = targetColour[i].blue  = 0;
@@ -97,7 +97,7 @@ static void fade_colour(int16_t *cur, const int16_t *target, int *changed)
 
 void fader_update(void)
 {
-	for(uint32_t i = 0; i < NUM_MODULES; i++) {
+	for(uint32_t i = 0; i < ws2801_num_modules; i++) {
 		fade_colour(&(curColour[i].red), &(targetColour[i].red), &somethingChanged);
 		fade_colour(&(curColour[i].green), &(targetColour[i].green), &somethingChanged);
 		fade_colour(&(curColour[i].blue), &(targetColour[i].blue), &somethingChanged);
diff --git a/src/main.cpp b/src/main.cpp
index 3ffbbc8..d45076c 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -64,7 +64,7 @@ void setup()
 
 	ws2801_udp_setup();
 
-	for(int i = 0; i < NUM_MODULES; i++) {
+	for(int i = 0; i < MAX_NUM_MODULES; i++) {
 		fader_set_colour(i, 0, 0, 0);
 		fader_fade_colour(i, 0, 255, 0);
 	}
@@ -93,15 +93,15 @@ void loop()
 		if((fader_loop % 200) == 0) {
 			int round = (fader_loop / 200) % 3;
 			if(round == 0) {
-				for(int i = 0; i < NUM_MODULES; i++) {
+				for(int i = 0; i < MAX_NUM_MODULES; i++) {
 					fader_fade_colour(i, 255, 0, 0);
 				}
 			} else if(round == 1) {
-				for(int i = 0; i < NUM_MODULES; i++) {
+				for(int i = 0; i < MAX_NUM_MODULES; i++) {
 					fader_fade_colour(i, 0, 255, 0);
 				}
 			} else {
-				for(int i = 0; i < NUM_MODULES; i++) {
+				for(int i = 0; i < MAX_NUM_MODULES; i++) {
 					fader_fade_colour(i, 0, 0, 255);
 				}
 			}
diff --git a/src/ws2801.cpp b/src/ws2801.cpp
index 8a853ae..504b3cd 100644
--- a/src/ws2801.cpp
+++ b/src/ws2801.cpp
@@ -2,10 +2,14 @@
 
 #include "ws2801.h"
 
-uint8_t message[3 * NUM_MODULES];
+uint8_t message[3 * MAX_NUM_MODULES];
+
+uint32_t ws2801_num_modules;
 
 void ws2801_init(void)
 {
+	ws2801_num_modules = MAX_NUM_MODULES;
+
 	SPI.begin();
 }
 
@@ -20,10 +24,16 @@ void ws2801_send_update(void)
 {
 	SPI.beginTransaction(SPISettings(1000000, MSBFIRST, SPI_MODE0));
 
-	for(uint32_t i = 0; i < 3*NUM_MODULES; i++) {
+	for(uint32_t i = 0; i < 3*ws2801_num_modules; i++) {
 		SPI.transfer(message[i]);
 	}
 
 	SPI.endTransaction();
 }
 
+void ws2801_set_num_modules(uint32_t n)
+{
+	if(n <= MAX_NUM_MODULES) {
+		ws2801_num_modules = n;
+	}
+}
diff --git a/src/ws2801.h b/src/ws2801.h
index ba34923..905f646 100644
--- a/src/ws2801.h
+++ b/src/ws2801.h
@@ -3,10 +3,13 @@
 
 #include <stdint.h>
 
-#define NUM_MODULES 32
+#define MAX_NUM_MODULES 255
+
+extern uint32_t ws2801_num_modules;
 
 void ws2801_init(void);
 void ws2801_set_colour(uint32_t module, uint8_t red, uint8_t green, uint8_t blue);
 void ws2801_send_update(void);
+void ws2801_set_num_modules(uint32_t n);
 
 #endif // WS2801_H
diff --git a/src/ws2801_udp.cpp b/src/ws2801_udp.cpp
index 5ecad4d..59e3b95 100644
--- a/src/ws2801_udp.cpp
+++ b/src/ws2801_udp.cpp
@@ -16,7 +16,8 @@ enum {
 	SET_COLOUR = 0,
 	FADE_COLOUR = 1,
 	ADD_COLOUR = 2,
-	SET_FADESTEP = 3
+	SET_FADESTEP = 3,
+	SET_NUM_MODULES = 4
 };
 
 void ws2801_udp_setup(void)
@@ -40,16 +41,6 @@ void ws2801_udp_loop(void)
 	int packetSize = ws2801UDP.parsePacket();
 	if(packetSize)
 	{
-		/*
-		Serial.print("Received packet of size ");
-		Serial.println(packetSize);
-		Serial.print("From ");
-		IPAddress remoteIp = ws2801UDP.remoteIP();
-		Serial.print(remoteIp);
-		Serial.print(", port ");
-		Serial.println(ws2801UDP.remotePort());
-		*/
-
 		// read the packet into packetBufffer
 		while((len = ws2801UDP.read(cmd, WS2801_CMD_LEN)) == WS2801_CMD_LEN) {
 			action = cmd[0];
@@ -58,7 +49,7 @@ void ws2801_udp_loop(void)
 			g      = cmd[3];
 			b      = cmd[4];
 
-			if(module >= NUM_MODULES) {
+			if(module >= ws2801_num_modules) {
 				// module index out of range
 				continue;
 			}
@@ -80,6 +71,10 @@ void ws2801_udp_loop(void)
 					fader_set_fadestep(r); // red channel contains the fadestep in this case
 					break;
 
+				case SET_NUM_MODULES:
+					// red and green channels contain the number of modules, big endian
+					ws2801_set_num_modules(((uint32_t)r << 16) + ((uint32_t)g << 8) + b);
+
 				default:
 					//Serial.println("WS2801UDP: ERROR: invalid action received!");
 					break;