diff --git a/gcode.c b/gcode.c
index 323b8a8..10ccad4 100644
--- a/gcode.c
+++ b/gcode.c
@@ -89,7 +89,7 @@ typedef struct {
   int16_t spindle_speed;         /* RPM/100 */
   uint8_t plane_axis_0, plane_axis_1, plane_axis_2; // The axes of the selected plane  
 } parser_state_t;
-parser_state_t gc;
+static parser_state_t gc;
 
 #define FAIL(status) gc.status_code = status;
 
diff --git a/serial_protocol.c b/serial_protocol.c
index 25fca16..6e6fd75 100644
--- a/serial_protocol.c
+++ b/serial_protocol.c
@@ -28,8 +28,8 @@
 #include <avr/pgmspace.h>
 #define LINE_BUFFER_SIZE 50
 
-char line[LINE_BUFFER_SIZE];
-uint8_t char_counter;
+static char line[LINE_BUFFER_SIZE];
+static uint8_t char_counter;
 
 void prompt() {
   printPgmString(PSTR("ok\r\n"));
diff --git a/stepper.c b/stepper.c
index 834696a..a73ac14 100644
--- a/stepper.c
+++ b/stepper.c
@@ -39,21 +39,21 @@ void set_step_events_per_minute(uint32_t steps_per_minute);
 #define MINIMUM_STEPS_PER_MINUTE 1200
 #define CYCLES_PER_ACCELERATION_TICK ((TICKS_PER_MICROSECOND*1000000)/ACCELERATION_TICKS_PER_SECOND)
 
-block_t *current_block;    // A convenience pointer to the block currently being traced
+static block_t *current_block;  // A convenience pointer to the block currently being traced
 
 // Variables used by The Stepper Driver Interrupt
-uint8_t out_bits;               // The next stepping-bits to be output
-int32_t counter_x, 
-        counter_y, 
-        counter_z;              // counter variables for the bresenham line tracer
-uint32_t step_events_completed; // The number of step events executed in the current block
-volatile int busy;              // TRUE when SIG_OUTPUT_COMPARE1A is being serviced. Used to avoid retriggering that handler.
+static uint8_t out_bits;        // The next stepping-bits to be output
+static int32_t counter_x,       // Counter variables for the bresenham line tracer
+               counter_y, 
+               counter_z;       
+static uint32_t step_events_completed; // The number of step events executed in the current block
+volatile int busy; // TRUE when SIG_OUTPUT_COMPARE1A is being serviced. Used to avoid retriggering that handler.
 
 // Variables used by the trapezoid generation
-uint32_t cycles_per_step_event;        // The number of machine cycles between each step event
-uint32_t trapezoid_tick_cycle_counter; // The cycles since last trapezoid_tick. Used to generate ticks at a steady
-                                       // pace without allocating a separate timer
-uint32_t trapezoid_adjusted_rate;      // The current rate of step_events according to the trapezoid generator
+static uint32_t cycles_per_step_event;        // The number of machine cycles between each step event
+static uint32_t trapezoid_tick_cycle_counter; // The cycles since last trapezoid_tick. Used to generate ticks at a steady
+                                              // pace without allocating a separate timer
+static uint32_t trapezoid_adjusted_rate;      // The current rate of step_events according to the trapezoid generator
 
 // Two trapezoids:
 //         __________________________
diff --git a/stepper_plan.c b/stepper_plan.c
index 0d6a7c2..613e745 100644
--- a/stepper_plan.c
+++ b/stepper_plan.c
@@ -60,10 +60,11 @@
 #include "config.h"
 #include "wiring_serial.h"
 
-block_t block_buffer[BLOCK_BUFFER_SIZE]; // A ring buffer for motion instructions
+block_t block_buffer[BLOCK_BUFFER_SIZE];  // A ring buffer for motion instructions
 volatile int block_buffer_head;           // Index of the next block to be pushed
 volatile int block_buffer_tail;           // Index of the block to process now
-uint8_t acceleration_management;          // Acceleration management active?
+
+static uint8_t acceleration_management;   // Acceleration management active?
 
 
 // NOTE: See bottom of this module for a comment outlining the reasoning behind the mathematics of the