diff --git a/planner.c b/planner.c
index 16566bc..d1109bd 100644
--- a/planner.c
+++ b/planner.c
@@ -64,11 +64,11 @@
 #include "wiring_serial.h"
 
 // The number of linear motions that can be in the plan at any give time
-#define BLOCK_BUFFER_SIZE 20  
+#define BLOCK_BUFFER_SIZE 16
 
 static block_t block_buffer[BLOCK_BUFFER_SIZE];  // A ring buffer for motion instructions
-static volatile int block_buffer_head;           // Index of the next block to be pushed
-static volatile int block_buffer_tail;           // Index of the block to process now
+static volatile uint8_t block_buffer_head;           // Index of the next block to be pushed
+static volatile uint8_t block_buffer_tail;           // Index of the block to process now
 
 // The current position of the tool in absolute steps
 static int32_t position[3];   
diff --git a/wiring_serial.c b/wiring_serial.c
index 20f8756..5109d39 100644
--- a/wiring_serial.c
+++ b/wiring_serial.c
@@ -31,12 +31,12 @@
 // using a ring buffer (I think), in which rx_buffer_head is the index of the
 // location to which to write the next incoming character and rx_buffer_tail
 // is the index of the location from which to read.
-#define RX_BUFFER_SIZE 200
+#define RX_BUFFER_SIZE 256
 
 unsigned char rx_buffer[RX_BUFFER_SIZE];
 
-int rx_buffer_head = 0;
-int rx_buffer_tail = 0;
+uint8_t rx_buffer_head = 0;
+uint8_t rx_buffer_tail = 0;
 
 void beginSerial(long baud)
 {