diff --git a/libraries/gdtoa/gdtoa.h b/libraries/gdtoa/gdtoa.h
index 8b7390a28..516e6a68c 100644
--- a/libraries/gdtoa/gdtoa.h
+++ b/libraries/gdtoa/gdtoa.h
@@ -48,20 +48,15 @@ THIS SOFTWARE.
  * compiling to deal with, which means we can't run the generation
  * program on the target.
  */
-#if defined(__x86_64__)
+#if defined(__x86_64__) || defined(__arm64__)
 #define IEEE_8087
 #define Arith_Kind_ASL 1
 #define Long int
 #define Intcast (int)(long)
 #define Double_Align
 #define X64_bit_pointers
-#elif defined(__i386__)
-#define IEEE_8087
-#define Arith_Kind_ASL 1
 #else
-#define IEEE_MC68k
-#define Arith_Kind_ASL 2
-#define Double_Align
+#error Unsupported architecture
 #endif
 #else
 #include "arith.h"
diff --git a/libraries/gdtoa/gdtoaimp.h b/libraries/gdtoa/gdtoaimp.h
index c63bf3135..ae7eeb572 100644
--- a/libraries/gdtoa/gdtoaimp.h
+++ b/libraries/gdtoa/gdtoaimp.h
@@ -202,7 +202,7 @@ THIS SOFTWARE.
  * all ia32 compilers had phased out extended precision.
  */
 #elif defined(__APPLE__)
-#if defined(__x86_64__) || defined(__i386__)
+#if defined(__x86_64__) || defined(__arm64__)
 #define f_QNAN 0xffc00000
 #define d_QNAN0 0x0
 #define d_QNAN1 0xfff80000
@@ -216,18 +216,7 @@ THIS SOFTWARE.
 #define ldus_QNAN3 0xc000
 #define ldus_QNAN4 0xffff
 #else
-#define f_QNAN 0xffc00000
-#define d_QNAN0 0xfff80000
-#define d_QNAN1 0x0
-#define ld_QNAN0 0xfff80000
-#define ld_QNAN1 0x0
-#define ld_QNAN2 0x0
-#define ld_QNAN3 0x0
-#define ldus_QNAN0 0xfff8
-#define ldus_QNAN1 0x0
-#define ldus_QNAN2 0x0
-#define ldus_QNAN3 0x0
-#define ldus_QNAN4 0x0
+#error Unsupported architecture
 #endif
 #else
 #include "gd_qnan.h"