diff --git a/gcode_parse.c b/gcode_parse.c
index 1eb4eb0..16c4992 100644
--- a/gcode_parse.c
+++ b/gcode_parse.c
@@ -14,6 +14,9 @@
 #include	"sersendf.h"
 
 #include	"gcode_process.h"
+#ifdef SIMULATOR
+  #include "simulator.h"
+#endif
 
 /// current or previous gcode word
 /// for working out what to do with data just received
@@ -102,7 +105,9 @@ void gcode_parse_char(uint8_t c) {
 	// uppercase
 	if (c >= 'a' && c <= 'z')
 		c &= ~32;
-
+#ifdef SIMULATOR
+  record_comment_stream(c);
+#endif
 	// process previous field
 	if (last_field) {
 		// check if we're seeing a new field or end of line
diff --git a/simulator.h b/simulator.h
index 13d254d..33830d2 100644
--- a/simulator.h
+++ b/simulator.h
@@ -45,6 +45,7 @@
 
 #include <stdint.h>
 #include <stdbool.h>
+#include "simulator/data_recorder.h"
 
 #define PROGMEM
 #define PGM_P const char *
diff --git a/simulator/data_recorder.c b/simulator/data_recorder.c
index b181dc9..c0d6170 100644
--- a/simulator/data_recorder.c
+++ b/simulator/data_recorder.c
@@ -50,7 +50,31 @@ void record_pin(int pin, bool state, uint32_t t) {
   // Naive format: each line contains all values, beginning with the time
   fprintf(file, "%u", t);
   for (int i = 0; i < pin_count; i++)
-    fprintf(file, "\t%u", values[i]);
+    fprintf(file, " %u", values[i]);
   fprintf(file, "\n");
   fflush(file);
 }
+
+static char comment_buffer[300];
+static int comment_buffer_index;
+void record_comment_stream(char ch) {
+  // Got CR, LF or buffer full
+  if ( comment_buffer_index == sizeof(comment_buffer)-1 ||
+       ch == '\r' || ch == '\n' || ch == 0 ) {
+
+    // Terminate string, reset buffer, emit comment
+    comment_buffer[comment_buffer_index] = 0;
+    comment_buffer_index = 0;
+    record_comment(comment_buffer);
+    if (ch == '\r' || ch == '\n')
+      return;
+  }
+
+  // Acumulate char from stream
+  comment_buffer[comment_buffer_index++] = ch;
+}
+
+void record_comment(const char * msg) {
+  fprintf(file, "; %s\n", msg);
+  fflush(file);
+}
diff --git a/simulator/data_recorder.h b/simulator/data_recorder.h
index cf20acf..067cdb6 100644
--- a/simulator/data_recorder.h
+++ b/simulator/data_recorder.h
@@ -8,5 +8,7 @@
 void recorder_init(const char* filename);
 void record_pin(int pin, bool state, uint32_t time);
 void add_trace_var(const char* name, int pin);
+void record_comment(const char * msg);
+void record_comment_stream(char ch);
 
 #endif /* DATA_RECORDER_H_ */