diff --git a/spi.cpp b/spi.cpp
index 73c75f0..5afcffb 100644
--- a/spi.cpp
+++ b/spi.cpp
@@ -162,11 +162,11 @@ void spi_n(uint8_t value, uint16_t cnt)
 	while (cnt--) spi_b(value);
 }
 
-void spi_read(uint8_t *addr, uint16_t len, int wide)
+void spi_read(uint8_t *addr, uint32_t len, int wide)
 {
 	if (wide)
 	{
-		uint16_t len16 = len >> 1;
+		uint32_t len16 = len >> 1;
 		uint16_t *a16 = (uint16_t*)addr;
 		while (len16--) *a16++ = spi_w(0);
 		if (len & 1) *((uint8_t*)a16) = spi_w(0);
@@ -177,11 +177,11 @@ void spi_read(uint8_t *addr, uint16_t len, int wide)
 	}
 }
 
-void spi_write(const uint8_t *addr, uint16_t len, int wide)
+void spi_write(const uint8_t *addr, uint32_t len, int wide)
 {
 	if (wide)
 	{
-		uint16_t len16 = len >> 1;
+		uint32_t len16 = len >> 1;
 		uint16_t *a16 = (uint16_t*)addr;
 		while (len16--) spi_w(*a16++);
 		if(len & 1) spi_w(*((uint8_t*)a16));
diff --git a/spi.h b/spi.h
index e013941..55bb4c5 100644
--- a/spi.h
+++ b/spi.h
@@ -39,8 +39,8 @@ void spi32_b(uint32_t parm);
 uint32_t spi32_w(uint32_t parm);
 
 /* block transfer functions */
-void spi_read(uint8_t *addr, uint16_t len, int wide);
-void spi_write(const uint8_t *addr, uint16_t len, int wide);
+void spi_read(uint8_t *addr, uint32_t len, int wide);
+void spi_write(const uint8_t *addr, uint32_t len, int wide);
 void spi_block_read(uint8_t *addr, int wide, int sz = 512);
 void spi_block_write(const uint8_t *addr, int wide, int sz = 512);
 
diff --git a/support/arcade/mra_loader.cpp b/support/arcade/mra_loader.cpp
index 0aa7211..3f578a8 100644
--- a/support/arcade/mra_loader.cpp
+++ b/support/arcade/mra_loader.cpp
@@ -340,7 +340,7 @@ static void rom_finish(int send, uint32_t address, int index)
 				{
 					ProgressMessage("Sending", str, len - romlen[0], len);
 
-					uint16_t chunk = (romlen[0] > 4096) ? 4096 : romlen[0];
+					uint32_t chunk = (romlen[0] > 4096) ? 4096 : romlen[0];
 					user_io_file_tx_data(data, chunk);
 
 					romlen[0] -= chunk;
diff --git a/user_io.cpp b/user_io.cpp
index 16a9113..c8cea82 100644
--- a/user_io.cpp
+++ b/user_io.cpp
@@ -1446,7 +1446,7 @@ void user_io_set_download(unsigned char enable, int addr)
 	DisableFpga();
 }
 
-void user_io_file_tx_data(const uint8_t *addr, uint16_t len)
+void user_io_file_tx_data(const uint8_t *addr, uint32_t len)
 {
 	EnableFpga();
 	spi8(FIO_FILE_TX_DAT);
@@ -1467,7 +1467,7 @@ void user_io_set_upload(unsigned char enable, int addr)
 	DisableFpga();
 }
 
-void user_io_file_rx_data(uint8_t *addr, uint16_t len)
+void user_io_file_rx_data(uint8_t *addr, uint32_t len)
 {
 	EnableFpga();
 	spi8(FIO_FILE_TX_DAT);
@@ -2036,7 +2036,7 @@ int user_io_file_tx_a(const char* name, uint16_t index)
 	if (use_progress) ProgressMessage(0, 0, 0, 0);
 	while (bytes2send)
 	{
-		uint16_t chunk = (bytes2send > sizeof(buf)) ? sizeof(buf) : bytes2send;
+		uint32_t chunk = (bytes2send > sizeof(buf)) ? sizeof(buf) : bytes2send;
 
 		FileReadAdv(&f, buf, chunk);
 		user_io_file_tx_data(buf, chunk);
@@ -2127,7 +2127,7 @@ int user_io_file_tx(const char* name, unsigned char index, char opensave, char m
 				uint32_t sz = fb.size;
 				while (sz)
 				{
-					uint16_t chunk = (sz > sizeof(buf)) ? sizeof(buf) : sz;
+					uint32_t chunk = (sz > sizeof(buf)) ? sizeof(buf) : sz;
 					FileReadAdv(&fb, buf, chunk);
 					user_io_file_tx_data(buf, chunk);
 					sz -= chunk;
@@ -2193,7 +2193,7 @@ int user_io_file_tx(const char* name, unsigned char index, char opensave, char m
 				uint32_t sz = fg.size;
 				while (sz)
 				{
-					uint16_t chunk = (sz > sizeof(buf)) ? sizeof(buf) : sz;
+					uint32_t chunk = (sz > sizeof(buf)) ? sizeof(buf) : sz;
 					FileReadAdv(&fg, buf, chunk);
 					user_io_file_tx_data(buf, chunk);
 					sz -= chunk;
@@ -2227,7 +2227,7 @@ int user_io_file_tx(const char* name, unsigned char index, char opensave, char m
 	{
 		while (dosend && bytes2send)
 		{
-			uint16_t chunk = (bytes2send > sizeof(buf)) ? sizeof(buf) : bytes2send;
+			uint32_t chunk = (bytes2send > sizeof(buf)) ? sizeof(buf) : bytes2send;
 
 			FileReadAdv(&f, buf, chunk);
 			if (is_snes() && is_snes_bs) snes_patch_bs_header(&f, buf);
diff --git a/user_io.h b/user_io.h
index 52824cf..d69755b 100644
--- a/user_io.h
+++ b/user_io.h
@@ -227,9 +227,9 @@ unsigned char user_io_ext_idx(char *, char*);
 void user_io_set_index(unsigned char index);
 void user_io_set_aindex(uint16_t index);
 void user_io_set_download(unsigned char enable, int addr = 0);
-void user_io_file_tx_data(const uint8_t *addr, uint16_t len);
+void user_io_file_tx_data(const uint8_t *addr, uint32_t len);
 void user_io_set_upload(unsigned char enable, int addr = 0);
-void user_io_file_rx_data(uint8_t *addr, uint16_t len);
+void user_io_file_rx_data(uint8_t *addr, uint32_t len);
 void user_io_file_info(const char *ext);
 int user_io_get_width();