diff --git a/include/fast_float/ascii_number.h b/include/fast_float/ascii_number.h
index 9b5befe..a70db6e 100644
--- a/include/fast_float/ascii_number.h
+++ b/include/fast_float/ascii_number.h
@@ -28,11 +28,20 @@ template <typename UC> fastfloat_really_inline constexpr bool has_simd_opt() {
 #endif
 }
 
+template <typename value_type> struct get_equal_sized_uint {
+  using type = std::conditional_t<
+      sizeof(value_type) == 4, uint32_t,
+      std::conditional_t<sizeof(value_type) == 2, uint16_t, uint8_t>>;
+};
+
+template <typename value_type>
+using get_equal_sized_uint_t = typename get_equal_sized_uint<value_type>::type;
+
 // Next function can be micro-optimized, but compilers are entirely
 // able to optimize it well.
 template <typename UC>
 fastfloat_really_inline constexpr bool is_integer(UC c) noexcept {
-  return static_cast<uint8_t>(c - UC('0')) < 10;
+  return static_cast<get_equal_sized_uint_t<UC>>(c - UC('0')) < 10;
 }
 
 fastfloat_really_inline constexpr uint64_t byteswap(uint64_t val) {