diff --git a/include/fast_float/ascii_number.h b/include/fast_float/ascii_number.h
index fbcc5f9..39c8d67 100644
--- a/include/fast_float/ascii_number.h
+++ b/include/fast_float/ascii_number.h
@@ -7,11 +7,13 @@
 #include <cstring>
 #include <iterator>
 
-#if defined(__has_include) && __has_include(<version>)
-#include <version>
-#if defined(__cpp_lib_bit_cast)
-#include <bit>
-#endif
+#if defined __has_include
+  #if __has_include(<version>)
+    #include <version>
+    #if defined(__cpp_lib_bit_cast)
+      #include <bit>
+    #endif
+  #endif
 #endif
 
 #include "float_common.h"
diff --git a/include/fast_float/fast_float.h b/include/fast_float/fast_float.h
index ac18297..1efe917 100644
--- a/include/fast_float/fast_float.h
+++ b/include/fast_float/fast_float.h
@@ -4,13 +4,17 @@
 
 #include <system_error>
 
-#if !defined(CXX20_CONSTEXPR) && defined(__has_include) && __has_include(<version>)
-#include <version>
-#if defined(__cpp_lib_bit_cast)
-#define CXX20_CONSTEXPR constexpr
-#else
-#define CXX20_CONSTEXPR
-#endif
+#if !defined(CXX20_CONSTEXPR)
+  #define CXX20_CONSTEXPR
+  #if defined __has_include
+    #if __has_include(<version>)
+      #include <version>
+      #if defined(__cpp_lib_bit_cast)
+        #undef CXX20_CONSTEXPR
+        #define CXX20_CONSTEXPR constexpr
+      #endif
+    #endif
+  #endif
 #endif
 
 namespace fast_float {
diff --git a/include/fast_float/float_common.h b/include/fast_float/float_common.h
index 1e10bf8..9ce20a8 100644
--- a/include/fast_float/float_common.h
+++ b/include/fast_float/float_common.h
@@ -73,13 +73,17 @@
 #define fastfloat_really_inline inline __attribute__((always_inline))
 #endif
 
-#if !defined(CXX20_CONSTEXPR) && defined(__has_include) && __has_include(<version>)
-#include <version>
-#if defined(__cpp_lib_bit_cast)
-#define CXX20_CONSTEXPR constexpr
-#else
-#define CXX20_CONSTEXPR
-#endif
+#if !defined(CXX20_CONSTEXPR)
+  #define CXX20_CONSTEXPR
+  #if defined __has_include
+    #if __has_include(<version>)
+      #include <version>
+      #if defined(__cpp_lib_bit_cast)
+        #undef CXX20_CONSTEXPR
+        #define CXX20_CONSTEXPR constexpr
+      #endif
+    #endif
+  #endif
 #endif
 
 namespace fast_float {