diff --git a/src/stage1/parse_f128.c b/src/stage1/parse_f128.c
index 9b5c287a3c..59750f2129 100644
--- a/src/stage1/parse_f128.c
+++ b/src/stage1/parse_f128.c
@@ -10,6 +10,28 @@
 #include <string.h>
 #include <math.h>
 
+// Every OSes seem to define endianness macros in different files.
+#if defined(__APPLE__)
+  #include <machine/endian.h>
+  #define ZIG_BIG_ENDIAN    BIG_ENDIAN
+  #define ZIG_LITTLE_ENDIAN LITTLE_ENDIAN
+  #define ZIG_BYTE_ORDER    BYTE_ORDER
+#elif defined(__DragonFly__) || defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__)
+  #include <sys/endian.h>
+  #define ZIG_BIG_ENDIAN    _BIG_ENDIAN
+  #define ZIG_LITTLE_ENDIAN _LITTLE_ENDIAN
+  #define ZIG_BYTE_ORDER    _BYTE_ORDER
+#elif defined(_WIN32) || defined(_WIN64)
+  // Assume that Windows installations are always little endian.
+  #define ZIG_LITTLE_ENDIAN 1
+  #define ZIG_BYTE_ORDER    ZIG_LITTLE_ENDIAN
+#else // Linux
+  #include <endian.h>
+  #define ZIG_BIG_ENDIAN    __BIG_ENDIAN
+  #define ZIG_LITTLE_ENDIAN __LITTLE_ENDIAN
+  #define ZIG_BYTE_ORDER    __BYTE_ORDER
+#endif
+
 #define shcnt(f) ((f)->shcnt + ((f)->rpos - (f)->buf))
 #define shlim(f, lim) __shlim((f), (lim))
 #define shgetc(f) (((f)->rpos != (f)->shend) ? *(f)->rpos++ : __shgetc(f))
@@ -47,8 +69,7 @@
 
 #define DECIMAL_DIG 36
 
-
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if defined(ZIG_BYTE_ORDER) && ZIG_BYTE_ORDER == ZIG_LITTLE_ENDIAN
 union ldshape {
     float128_t f;
     struct {
@@ -62,7 +83,7 @@ union ldshape {
         uint64_t hi;
     } i2;
 };
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif defined(ZIG_BYTE_ORDER) && ZIG_BYTE_ORDER == ZIG_BIG_ENDIAN
 union ldshape {
     float128_t f;
     struct {
@@ -76,6 +97,7 @@ union ldshape {
         uint64_t lo;
     } i2;
 };
+#else
 #error Unsupported endian
 #endif