diff --git a/os/various/chprintf.c b/os/various/chprintf.c
index 36dad0de9..2756e9cc8 100644
--- a/os/various/chprintf.c
+++ b/os/various/chprintf.c
@@ -32,7 +32,7 @@
 #include "memstreams.h"
 
 #define MAX_FILLER 11
-#define FLOAT_PRECISION 5
+#define FLOAT_PRECISION 9
 
 static char *long_to_string_with_divisor(char *p,
                                          long num,
@@ -73,14 +73,13 @@ static char *ltoa(char *p, long num, unsigned radix) {
 }
 
 #if CHPRINTF_USE_FLOAT
-static long pow10[] = {10, 100, 1000, 10000, 100000, 1000000, 10000000,
-                       100000000, 1000000000, 10000000000, 100000000000,
-                       1000000000000, 10000000000000};
+static long pow10[FLOAT_PRECISION] = {10, 100, 1000, 10000, 100000, 1000000,
+                                      10000000, 100000000, 1000000000};
 
 static char *ftoa(char *p, double num, unsigned long precision) {
   long l;
 
-  if (precision == 0)
+  if ((precision == 0) || (precision > FLOAT_PRECISION))
     precision = FLOAT_PRECISION;
   precision = pow10[precision - 1];