diff --git a/teensy3/serial1.c b/teensy3/serial1.c
index ab32d3cc9..154b1f2e2 100644
--- a/teensy3/serial1.c
+++ b/teensy3/serial1.c
@@ -79,14 +79,20 @@ static volatile uint8_t transmitting = 0;
   #define rts_assert()        *(rts_pin+8) = rts_mask;
   #define rts_deassert()      *(rts_pin+4) = rts_mask;
 #endif
-#if SERIAL1_TX_BUFFER_SIZE > 255
+#if SERIAL1_TX_BUFFER_SIZE > 65535
+static volatile uint32_t tx_buffer_head = 0;
+static volatile uint32_t tx_buffer_tail = 0;
+#elif SERIAL1_TX_BUFFER_SIZE > 255
 static volatile uint16_t tx_buffer_head = 0;
 static volatile uint16_t tx_buffer_tail = 0;
 #else
 static volatile uint8_t tx_buffer_head = 0;
 static volatile uint8_t tx_buffer_tail = 0;
 #endif
-#if SERIAL1_RX_BUFFER_SIZE > 255
+#if SERIAL1_RX_BUFFER_SIZE > 65535
+static volatile uint32_t rx_buffer_head = 0;
+static volatile uint32_t rx_buffer_tail = 0;
+#elif SERIAL1_RX_BUFFER_SIZE > 255
 static volatile uint16_t rx_buffer_head = 0;
 static volatile uint16_t rx_buffer_tail = 0;
 #else
diff --git a/teensy3/serial2.c b/teensy3/serial2.c
index 679d6eaa6..78deab7ba 100644
--- a/teensy3/serial2.c
+++ b/teensy3/serial2.c
@@ -78,14 +78,20 @@ static volatile uint8_t transmitting = 0;
   #define rts_assert()        *(rts_pin+8) = rts_mask;
   #define rts_deassert()      *(rts_pin+4) = rts_mask;
 #endif
-#if SERIAL2_TX_BUFFER_SIZE > 255
+#if SERIAL2_TX_BUFFER_SIZE > 65535
+static volatile uint32_t tx_buffer_head = 0;
+static volatile uint32_t tx_buffer_tail = 0;
+#elif SERIAL2_TX_BUFFER_SIZE > 255
 static volatile uint16_t tx_buffer_head = 0;
 static volatile uint16_t tx_buffer_tail = 0;
 #else
 static volatile uint8_t tx_buffer_head = 0;
 static volatile uint8_t tx_buffer_tail = 0;
 #endif
-#if SERIAL2_RX_BUFFER_SIZE > 255
+#if SERIAL2_RX_BUFFER_SIZE > 65535
+static volatile uint32_t rx_buffer_head = 0;
+static volatile uint32_t rx_buffer_tail = 0;
+#elif SERIAL2_RX_BUFFER_SIZE > 255
 static volatile uint16_t rx_buffer_head = 0;
 static volatile uint16_t rx_buffer_tail = 0;
 #else
diff --git a/teensy3/serial3.c b/teensy3/serial3.c
index f7e6c8234..b72b20bf7 100644
--- a/teensy3/serial3.c
+++ b/teensy3/serial3.c
@@ -79,14 +79,20 @@ static volatile uint8_t transmitting = 0;
   #define rts_assert()        *(rts_pin+8) = rts_mask;
   #define rts_deassert()      *(rts_pin+4) = rts_mask;
 #endif
-#if SERIAL3_TX_BUFFER_SIZE > 255
+#if SERIAL3_TX_BUFFER_SIZE > 65535
+static volatile uint32_t tx_buffer_head = 0;
+static volatile uint32_t tx_buffer_tail = 0;
+#elif SERIAL3_TX_BUFFER_SIZE > 255
 static volatile uint16_t tx_buffer_head = 0;
 static volatile uint16_t tx_buffer_tail = 0;
 #else
 static volatile uint8_t tx_buffer_head = 0;
 static volatile uint8_t tx_buffer_tail = 0;
 #endif
-#if SERIAL3_RX_BUFFER_SIZE > 255
+#if SERIAL3_RX_BUFFER_SIZE > 65535
+static volatile uint32_t rx_buffer_head = 0;
+static volatile uint32_t rx_buffer_tail = 0;
+#elif SERIAL3_RX_BUFFER_SIZE > 255
 static volatile uint16_t rx_buffer_head = 0;
 static volatile uint16_t rx_buffer_tail = 0;
 #else
diff --git a/teensy3/serial4.c b/teensy3/serial4.c
index 715139898..b6efefd6c 100644
--- a/teensy3/serial4.c
+++ b/teensy3/serial4.c
@@ -70,14 +70,20 @@ static volatile uint8_t *transmit_pin=NULL;
 static volatile uint8_t *rts_pin=NULL;
 #define rts_assert()        *rts_pin = 0
 #define rts_deassert()      *rts_pin = 1
-#if SERIAL4_TX_BUFFER_SIZE > 255
+#if SERIAL4_TX_BUFFER_SIZE > 65535
+static volatile uint32_t tx_buffer_head = 0;
+static volatile uint32_t tx_buffer_tail = 0;
+#elif SERIAL4_TX_BUFFER_SIZE > 255
 static volatile uint16_t tx_buffer_head = 0;
 static volatile uint16_t tx_buffer_tail = 0;
 #else
 static volatile uint8_t tx_buffer_head = 0;
 static volatile uint8_t tx_buffer_tail = 0;
 #endif
-#if SERIAL4_RX_BUFFER_SIZE > 255
+#if SERIAL4_RX_BUFFER_SIZE > 65535
+static volatile uint32_t rx_buffer_head = 0;
+static volatile uint32_t rx_buffer_tail = 0;
+#elif SERIAL4_RX_BUFFER_SIZE > 255
 static volatile uint16_t rx_buffer_head = 0;
 static volatile uint16_t rx_buffer_tail = 0;
 #else
diff --git a/teensy3/serial5.c b/teensy3/serial5.c
index 9bc1c03e9..e07162918 100644
--- a/teensy3/serial5.c
+++ b/teensy3/serial5.c
@@ -70,14 +70,20 @@ static volatile uint8_t *transmit_pin=NULL;
 static volatile uint8_t *rts_pin=NULL;
 #define rts_assert()        *rts_pin = 0
 #define rts_deassert()      *rts_pin = 1
-#if SERIAL5_TX_BUFFER_SIZE > 255
+#if SERIAL5_TX_BUFFER_SIZE > 65535
+static volatile uint32_t tx_buffer_head = 0;
+static volatile uint32_t tx_buffer_tail = 0;
+#elif SERIAL5_TX_BUFFER_SIZE > 255
 static volatile uint16_t tx_buffer_head = 0;
 static volatile uint16_t tx_buffer_tail = 0;
 #else
 static volatile uint8_t tx_buffer_head = 0;
 static volatile uint8_t tx_buffer_tail = 0;
 #endif
-#if SERIAL5_RX_BUFFER_SIZE > 255
+#if SERIAL5_RX_BUFFER_SIZE > 65535
+static volatile uint32_t rx_buffer_head = 0;
+static volatile uint32_t rx_buffer_tail = 0;
+#elif SERIAL5_RX_BUFFER_SIZE > 255
 static volatile uint16_t rx_buffer_head = 0;
 static volatile uint16_t rx_buffer_tail = 0;
 #else
diff --git a/teensy3/serial6.c b/teensy3/serial6.c
index a7b26a3f8..bdde8d23a 100644
--- a/teensy3/serial6.c
+++ b/teensy3/serial6.c
@@ -70,14 +70,20 @@ static volatile uint8_t *transmit_pin=NULL;
 static volatile uint8_t *rts_pin=NULL;
 #define rts_assert()        *rts_pin = 0
 #define rts_deassert()      *rts_pin = 1
-#if SERIAL6_TX_BUFFER_SIZE > 255
+#if SERIAL6_TX_BUFFER_SIZE > 65535
+static volatile uint32_t tx_buffer_head = 0;
+static volatile uint32_t tx_buffer_tail = 0;
+#elif SERIAL6_TX_BUFFER_SIZE > 255
 static volatile uint16_t tx_buffer_head = 0;
 static volatile uint16_t tx_buffer_tail = 0;
 #else
 static volatile uint8_t tx_buffer_head = 0;
 static volatile uint8_t tx_buffer_tail = 0;
 #endif
-#if SERIAL6_RX_BUFFER_SIZE > 255
+#if SERIAL6_RX_BUFFER_SIZE > 65535
+static volatile uint32_t rx_buffer_head = 0;
+static volatile uint32_t rx_buffer_tail = 0;
+#elif SERIAL6_RX_BUFFER_SIZE > 255
 static volatile uint16_t rx_buffer_head = 0;
 static volatile uint16_t rx_buffer_tail = 0;
 #else