diff --git a/include/fast_float/float_common.h b/include/fast_float/float_common.h
index 90eecc2..d2a99c0 100644
--- a/include/fast_float/float_common.h
+++ b/include/fast_float/float_common.h
@@ -34,12 +34,12 @@
 namespace fast_float {
 
 // The number of digits in the mantissa.
-typedef uint16_t am_digits;
+typedef uint_fast16_t am_digits;
 
 // The number of bits in the limb.
-typedef uint8_t limb_t;
+typedef uint_fast8_t limb_t;
 
-typedef uint8_t chars_format_t;
+typedef uint_fast8_t chars_format_t;
 
 enum class chars_format : chars_format_t;