diff --git a/gcode_parse.c b/gcode_parse.c
index e414d24..d4b7c5d 100644
--- a/gcode_parse.c
+++ b/gcode_parse.c
@@ -62,12 +62,16 @@ GCODE_COMMAND next_target		__attribute__ ((__section__ (".bss")));
 		multiplicand:  1..105000       (17 bit)
 		denominator:   1 or 10         ( 4 bit)
 */
+// accordingly:
+#define	DECFLOAT_EXP_MAX 4
+#define	DECFLOAT_MANT_MM_MAX 1048075
+#define	DECFLOAT_MANT_IN_MAX 32267
 
 /*
 	utility functions
 */
 extern const uint32_t powers[];  // defined in sermsg.c
-const int32_t rounding[DECFLOAT_EXP_MAX] = {0,  5,  50,  500,  5000,  50000,  500000};
+const int32_t rounding[DECFLOAT_EXP_MAX] = {0,  5,  50,  500};
 
 static int32_t decfloat_to_int(decfloat *df, int32_t multiplicand, uint32_t denominator) {
 	int32_t	r = df->mantissa;
@@ -292,10 +296,12 @@ void gcode_parse_char(uint8_t c) {
 
 			default:
 				// can't do ranges in switch..case, so process actual digits here.
-				if (    c >= '0'
-				     && c <= '9'
-				     && read_digit.mantissa < (DECFLOAT_MANT_MAX / 10)
-				     && read_digit.exponent < DECFLOAT_EXP_MAX ) {
+				if (c >= '0' && c <= '9' &&
+				    read_digit.exponent < DECFLOAT_EXP_MAX &&
+				    ((next_target.option_inches == 0 &&
+				      read_digit.mantissa < DECFLOAT_MANT_MM_MAX) ||
+				     (next_target.option_inches &&
+				      read_digit.mantissa < DECFLOAT_MANT_IN_MAX))){
 					// this is simply mantissa = (mantissa * 10) + atoi(c) in different clothes
 					read_digit.mantissa = (read_digit.mantissa << 3) + (read_digit.mantissa << 1) + (c - '0');
 					if (read_digit.exponent)
diff --git a/gcode_parse.h b/gcode_parse.h
index 3359cbb..a7021c8 100644
--- a/gcode_parse.h
+++ b/gcode_parse.h
@@ -18,16 +18,10 @@
 
 // this is a very crude decimal-based floating point structure.
 // a real floating point would at least have signed exponent.
-// max (DECFLOAT_EXP_MAX - 1) digits after decimal point, because point is
-// counted as well
-#define DECFLOAT_EXP_WIDTH 3					
-#define DECFLOAT_EXP_MAX  ((1 << DECFLOAT_EXP_WIDTH) - 1)
-#define DECFLOAT_MANT_WIDTH (32 - 1 - DECFLOAT_EXP_WIDTH)
-#define DECFLOAT_MANT_MAX (((uint32_t)1 << DECFLOAT_MANT_WIDTH) - 1)
 typedef struct {
 	uint32_t	sign			:1;
-	uint32_t	mantissa	:DECFLOAT_MANT_WIDTH;
-	uint32_t	exponent	:DECFLOAT_EXP_WIDTH;
+	uint32_t	mantissa	:28;
+	uint32_t	exponent	:3;
 } decfloat;
 
 // this holds all the possible data from a received command