diff --git a/include/fast_float/float_common.h b/include/fast_float/float_common.h
index 2801437..1a952c5 100644
--- a/include/fast_float/float_common.h
+++ b/include/fast_float/float_common.h
@@ -446,7 +446,7 @@ typedef int_fast8_t am_bits_t;
 
 // Power bias is signed for handling a denormal float
 // or an invalid mantissa.
-typedef int_fast16_t am_pow_t;
+typedef int16_t am_pow_t; // can't be int_fast16_t because invalid_am_bias hacks. Needs rewriting this.
 
 // Bias so we can get the real exponent with an invalid adjusted_mantissa.
 constexpr static am_pow_t invalid_am_bias = -0x8000;