diff --git a/gcode.c b/gcode.c
index 97a97b3..a68373e 100644
--- a/gcode.c
+++ b/gcode.c
@@ -264,7 +264,7 @@ uint8_t gc_execute_line(char *line)
         // Check for more than one command per modal group violations in the current block
         // NOTE: Variable 'word_bit' is always assigned, if the command is valid.
         if ( bit_istrue(command_words,bit(word_bit)) ) { FAIL(STATUS_GCODE_MODAL_GROUP_VIOLATION); }
-        bit_true(command_words,bit(word_bit));
+        command_words |= bit(word_bit);
         break;
         
       case 'M':
@@ -307,7 +307,7 @@ uint8_t gc_execute_line(char *line)
         // Check for more than one command per modal group violations in the current block
         // NOTE: Variable 'word_bit' is always assigned, if the command is valid.
         if ( bit_istrue(command_words,bit(word_bit)) ) { FAIL(STATUS_GCODE_MODAL_GROUP_VIOLATION); }
-        bit_true(command_words,bit(word_bit));
+        command_words |= bit(word_bit);
         break;
       
       // NOTE: All remaining letters assign values.
diff --git a/limits.c b/limits.c
index f6e5f01..030438e 100644
--- a/limits.c
+++ b/limits.c
@@ -86,7 +86,7 @@ ISR(LIMIT_INT_vect) // DEFAULT: Limit pin change interrupt process.
   if (sys.state != STATE_ALARM) { 
     if (bit_isfalse(sys.execute,EXEC_ALARM)) {
       mc_reset(); // Initiate system kill.
-      bit_true(sys.execute, (EXEC_ALARM | EXEC_CRIT_EVENT)); // Indicate hard limit critical event
+      bit_true_atomic(sys.execute, (EXEC_ALARM | EXEC_CRIT_EVENT)); // Indicate hard limit critical event
     }
   }
 }  
@@ -103,7 +103,7 @@ ISR(WDT_vect) // Watchdog timer ISR
       if (bit_istrue(settings.flags,BITFLAG_INVERT_LIMIT_PINS)) { bits ^= LIMIT_MASK; }
       if (bits & LIMIT_MASK) {
         mc_reset(); // Initiate system kill.
-        bit_true(sys.execute, (EXEC_ALARM | EXEC_CRIT_EVENT)); // Indicate hard limit critical event
+        bit_true_atomic(sys.execute, (EXEC_ALARM | EXEC_CRIT_EVENT)); // Indicate hard limit critical event
       }
     }  
   }
@@ -238,7 +238,7 @@ void limits_go_home(uint8_t cycle_mask)
   // Initiate pull-off using main motion control routines. 
   // TODO : Clean up state routines so that this motion still shows homing state.
   sys.state = STATE_QUEUED;
-  bit_true(sys.execute, EXEC_CYCLE_START);
+  bit_true_atomic(sys.execute, EXEC_CYCLE_START);
   protocol_execute_runtime();
   protocol_buffer_synchronize(); // Complete pull-off motion.
   
@@ -259,7 +259,7 @@ void limits_soft_check(float *target)
       // workspace volume so just come to a controlled stop so position is not lost. When complete
       // enter alarm mode.
       if (sys.state == STATE_CYCLE) {
-        bit_true(sys.execute, EXEC_FEED_HOLD);
+        bit_true_atomic(sys.execute, EXEC_FEED_HOLD);
         do {
           protocol_execute_runtime();
           if (sys.abort) { return; }
@@ -267,7 +267,7 @@ void limits_soft_check(float *target)
       }
       
       mc_reset(); // Issue system reset and ensure spindle and coolant are shutdown.
-      bit_true(sys.execute, (EXEC_ALARM | EXEC_CRIT_EVENT)); // Indicate soft limit critical event
+      bit_true_atomic(sys.execute, (EXEC_ALARM | EXEC_CRIT_EVENT)); // Indicate soft limit critical event
       protocol_execute_runtime(); // Execute to enter critical event loop and system abort
       return;
     
diff --git a/motion_control.c b/motion_control.c
index c57dfea..f3c8b2d 100644
--- a/motion_control.c
+++ b/motion_control.c
@@ -288,13 +288,13 @@ void mc_probe_cycle(float *target, float feed_rate, uint8_t invert_feed_rate)
   // NOTE: Parser error-checking ensures the probe isn't already closed/triggered.
   sys.probe_state = PROBE_ACTIVE;
 
-  bit_true(sys.execute, EXEC_CYCLE_START);
+  bit_true_atomic(sys.execute, EXEC_CYCLE_START);
   do {
     protocol_execute_runtime(); 
     if (sys.abort) { return; } // Check for system abort
   } while ((sys.state != STATE_IDLE) && (sys.state != STATE_QUEUED));
 
-  if (sys.probe_state == PROBE_ACTIVE) { bit_true(sys.execute, EXEC_CRIT_EVENT); }
+  if (sys.probe_state == PROBE_ACTIVE) { bit_true_atomic(sys.execute, EXEC_CRIT_EVENT); }
   protocol_execute_runtime();   // Check and execute run-time commands
   if (sys.abort) { return; } // Check for system abort
 
@@ -316,7 +316,7 @@ void mc_probe_cycle(float *target, float feed_rate, uint8_t invert_feed_rate)
   mc_line(target, feed_rate, invert_feed_rate); // Bypass mc_line(). Directly plan homing motion.
   #endif
 
-  bit_true(sys.execute, EXEC_CYCLE_START);
+  bit_true_atomic(sys.execute, EXEC_CYCLE_START);
   protocol_buffer_synchronize(); // Complete pull-off motion.
   if (sys.abort) { return; } // Did not complete. Alarm state set by mc_alarm.
 
@@ -337,7 +337,7 @@ void mc_reset()
 {
   // Only this function can set the system reset. Helps prevent multiple kill calls.
   if (bit_isfalse(sys.execute, EXEC_RESET)) {
-    bit_true(sys.execute, EXEC_RESET);
+    bit_true_atomic(sys.execute, EXEC_RESET);
 
     // Kill spindle and coolant.   
     spindle_stop();
@@ -348,7 +348,7 @@ void mc_reset()
     // the steppers enabled by avoiding the go_idle call altogether, unless the motion state is
     // violated, by which, all bets are off.
     if (sys.state & (STATE_CYCLE | STATE_HOLD | STATE_HOMING)) {
-      bit_true(sys.execute, EXEC_ALARM); // Flag main program to execute alarm state.
+      bit_true_atomic(sys.execute, EXEC_ALARM); // Flag main program to execute alarm state.
       st_go_idle(); // Force kill steppers. Position has likely been lost.
     }
   }
diff --git a/nuts_bolts.h b/nuts_bolts.h
index 5cab6f4..1417fa9 100644
--- a/nuts_bolts.h
+++ b/nuts_bolts.h
@@ -44,9 +44,11 @@
 
 // Bit field and masking macros
 #define bit(n) (1 << n) 
-#define bit_true(x,mask) {uint8_t sreg = SREG; cli(); (x) |= (mask); SREG = sreg; }
-#define bit_false(x,mask) {uint8_t sreg = SREG; cli(); (x) &= ~(mask); SREG = sreg; }
-#define bit_toggle(x,mask) {uint8_t sreg = SREG; cli(); (x) ^= (mask); SREG = sreg; }
+#define bit_true_atomic(x,mask) {uint8_t sreg = SREG; cli(); (x) |= (mask); SREG = sreg; }
+#define bit_false_atomic(x,mask) {uint8_t sreg = SREG; cli(); (x) &= ~(mask); SREG = sreg; }
+#define bit_toggle_atomic(x,mask) {uint8_t sreg = SREG; cli(); (x) ^= (mask); SREG = sreg; }
+#define bit_true(x,mask) (x) |= (mask)
+#define bit_false(x,mask) (x) &= ~(mask)
 #define bit_istrue(x,mask) ((x & mask) != 0)
 #define bit_isfalse(x,mask) ((x & mask) == 0)
 
diff --git a/protocol.c b/protocol.c
index 45f6c27..9507ca8 100644
--- a/protocol.c
+++ b/protocol.c
@@ -192,7 +192,7 @@ void protocol_execute_runtime()
         if (rt_exec & EXEC_ALARM) { report_alarm_message(ALARM_LIMIT_ERROR); }
         else { report_alarm_message(ALARM_PROBE_FAIL); }
         report_feedback_message(MESSAGE_CRITICAL_EVENT);
-        bit_false(sys.execute,EXEC_RESET); // Disable any existing reset
+        bit_false_atomic(sys.execute,EXEC_RESET); // Disable any existing reset
         do { 
           // Nothing. Block EVERYTHING until user issues reset or power cycles. Hard limits
           // typically occur while unattended or not paying attention. Gives the user time
@@ -208,7 +208,7 @@ void protocol_execute_runtime()
         // to indicate the possible severity of the problem.
         report_alarm_message(ALARM_ABORT_CYCLE);
       }
-      bit_false(sys.execute,(EXEC_ALARM | EXEC_CRIT_EVENT));
+      bit_false_atomic(sys.execute,(EXEC_ALARM | EXEC_CRIT_EVENT));
     } 
   
     // Execute system abort. 
@@ -220,7 +220,7 @@ void protocol_execute_runtime()
     // Execute and serial print status
     if (rt_exec & EXEC_STATUS_REPORT) { 
       report_realtime_status();
-      bit_false(sys.execute,EXEC_STATUS_REPORT);
+      bit_false_atomic(sys.execute,EXEC_STATUS_REPORT);
     }
     
     // Execute a feed hold with deceleration, only during cycle.
@@ -233,7 +233,7 @@ void protocol_execute_runtime()
         st_prep_buffer();
         sys.auto_start = false; // Disable planner auto start upon feed hold.
       }
-      bit_false(sys.execute,EXEC_FEED_HOLD);
+      bit_false_atomic(sys.execute,EXEC_FEED_HOLD);
     }
         
     // Execute a cycle start by starting the stepper interrupt begin executing the blocks in queue.
@@ -248,7 +248,7 @@ void protocol_execute_runtime()
           sys.auto_start = false; // Reset auto start per settings.
         }
       }    
-      bit_false(sys.execute,EXEC_CYCLE_START);
+      bit_false_atomic(sys.execute,EXEC_CYCLE_START);
     }
     
     // Reinitializes the cycle plan and stepper system after a feed hold for a resume. Called by 
@@ -259,7 +259,7 @@ void protocol_execute_runtime()
     if (rt_exec & EXEC_CYCLE_STOP) {
       if ( plan_get_current_block() ) { sys.state = STATE_QUEUED; }
       else { sys.state = STATE_IDLE; }
-      bit_false(sys.execute,EXEC_CYCLE_STOP);
+      bit_false_atomic(sys.execute,EXEC_CYCLE_STOP);
     }
 
   }
@@ -296,4 +296,4 @@ void protocol_buffer_synchronize()
 // NOTE: This function is called from the main loop and mc_line() only and executes when one of
 // two conditions exist respectively: There are no more blocks sent (i.e. streaming is finished, 
 // single commands), or the planner buffer is full and ready to go.
-void protocol_auto_cycle_start() { if (sys.auto_start) { bit_true(sys.execute, EXEC_CYCLE_START); } } 
+void protocol_auto_cycle_start() { if (sys.auto_start) { bit_true_atomic(sys.execute, EXEC_CYCLE_START); } } 
diff --git a/serial.c b/serial.c
index bcbffaa..9f352f5 100644
--- a/serial.c
+++ b/serial.c
@@ -157,9 +157,9 @@ ISR(SERIAL_RX)
   // Pick off runtime command characters directly from the serial stream. These characters are
   // not passed into the buffer, but these set system state flag bits for runtime execution.
   switch (data) {
-    case CMD_STATUS_REPORT: bit_true(sys.execute, EXEC_STATUS_REPORT); break; // Set as true
-    case CMD_CYCLE_START:   bit_true(sys.execute, EXEC_CYCLE_START); break; // Set as true
-    case CMD_FEED_HOLD:     bit_true(sys.execute, EXEC_FEED_HOLD); break; // Set as true
+    case CMD_STATUS_REPORT: bit_true_atomic(sys.execute, EXEC_STATUS_REPORT); break; // Set as true
+    case CMD_CYCLE_START:   bit_true_atomic(sys.execute, EXEC_CYCLE_START); break; // Set as true
+    case CMD_FEED_HOLD:     bit_true_atomic(sys.execute, EXEC_FEED_HOLD); break; // Set as true
     case CMD_RESET:         mc_reset(); break; // Call motion control reset routine.
     default: // Write character to buffer    
       next_head = rx_buffer_head + 1;
diff --git a/stepper.c b/stepper.c
index 496f916..b6f6fe0 100644
--- a/stepper.c
+++ b/stepper.c
@@ -342,7 +342,7 @@ ISR(TIMER1_COMPA_vect)
     } else {
       // Segment buffer empty. Shutdown.
       st_go_idle();
-      bit_true(sys.execute,EXEC_CYCLE_STOP); // Flag main program for cycle end
+      bit_true_atomic(sys.execute,EXEC_CYCLE_STOP); // Flag main program for cycle end
       return; // Nothing to do but exit.
     }  
   }