diff --git a/README.md b/README.md
index 17ddc85..938ba9b 100644
--- a/README.md
+++ b/README.md
@@ -380,15 +380,17 @@ int main() {
 
 ## You also can also use some additional options (currently only configure by macroses):
 
-There is a really common use case in mathematical and other abstract syntax tree (AST) like parsers,
-that already process sign and all other symbols before any number by itself. In this case you can 
-use FastFloat for only parse positive numbers in all supported formats with macros 
-`FASTFLOAT_ONLY_POSITIVE_C_NUMBER_WO_INF_NAN`, that significantly reduce the code size and improve
-performance. Additionally you can use macros `FASTFLOAT_ONLY_ROUNDS_TO_NEAREST_SUPPORTED` if you 
-only uneed `FE_TONEAREST` rounding mode in the parsing: this option is also improve performance a bit.
+There is a really common use case in mathematical and other abstract syntax tree (AST)-like parsers that already processes
+the sign and all other symbols before any number by itself. In this case you can use FastFloat to only parse positive numbers
+in all supported formats with macros `FASTFLOAT_ONLY_POSITIVE_C_NUMBER_WO_INF_NAN`, which significantly reduce the code size
+and improve performance. You also can use macros `FASTFLOAT_ISNOT_CHECKED_BOUNDS` if your code already checks bounds;
+it's very likely because all parsers need to check the first character by itself before parsing. Additionally, you can use
+macros `FASTFLOAT_ONLY_ROUNDS_TO_NEAREST_SUPPORTED` if you only need `FE_TONEAREST` rounding mode in the parsing;
+this option also improves performance a bit and reduces code size.
 
 ```C++
 #define FASTFLOAT_ONLY_POSITIVE_C_NUMBER_WO_INF_NAN
+#define FASTFLOAT_ISNOT_CHECKED_BOUNDS
 #define FASTFLOAT_ONLY_ROUNDS_TO_NEAREST_SUPPORTED
 #include "fast_float/fast_float.h"
 #include <iostream>
diff --git a/include/fast_float/parse_number.h b/include/fast_float/parse_number.h
index d7ec565..f3d5e3a 100644
--- a/include/fast_float/parse_number.h
+++ b/include/fast_float/parse_number.h
@@ -336,14 +336,16 @@ from_chars_float_advanced(UC const *first, UC const *last, T &value,
       ++first;
     }
   }
+#endif
+#ifdef FASTFLOAT_ISNOT_CHECKED_BOUNDS
+  // We are in parser code with external loop that checks bounds.
+  FASTFLOAT_ASSUME(first < last);
+#else
   if (first == last) {
     answer.ec = std::errc::invalid_argument;
     answer.ptr = first;
     return answer;
   }
-#else
-  // We are in parser code with external loop that checks bounds.
-  FASTFLOAT_ASSUME(first < last);
 #endif
   parsed_number_string_t<UC> const pns =
 #ifndef FASTFLOAT_ONLY_POSITIVE_C_NUMBER_WO_INF_NAN
@@ -498,19 +500,19 @@ from_chars_int_advanced(UC const *first, UC const *last, T &value,
   static_assert(is_supported_char_type<UC>::value,
                 "only char, wchar_t, char16_t and char32_t are supported");
 
-#ifdef FASTFLOAT_ONLY_POSITIVE_C_NUMBER_WO_INF_NAN
-  // We are in parser code with external loop that checks bounds.
-  FASTFLOAT_ASSUME(first < last);
-  // base is already checked in the parse_options_t constructor.
-#else
+#ifndef FASTFLOAT_ONLY_POSITIVE_C_NUMBER_WO_INF_NAN
   if (chars_format_t(options.format & chars_format::skip_white_space)) {
     while ((first != last) && fast_float::is_space(*first)) {
       ++first;
     }
   }
+#endif
+#ifdef FASTFLOAT_ISNOT_CHECKED_BOUNDS
+  // We are in parser code with external loop that checks bounds.
+  FASTFLOAT_ASSUME(first < last);
 #endif
   if (
-#ifndef FASTFLOAT_ONLY_POSITIVE_C_NUMBER_WO_INF_NAN
+#ifndef FASTFLOAT_ISNOT_CHECKED_BOUNDS
       first == last ||
 #endif
       options.base < 2 || options.base > 36) {