diff --git a/fixincludes/fixincl.x b/fixincludes/fixincl.x
index 47a3578f017..6cf22d19b2a 100644
--- a/fixincludes/fixincl.x
+++ b/fixincludes/fixincl.x
@@ -3480,6 +3480,43 @@ static const char* apzDarwin_Ucred__AtomicPatch[] = {
 #endif\n",
     (char*)NULL };
 
+/* * * * * * * * * * * * * * * * * * * * * * * * * *
+ *
+ *  Description of Darwin_Nix_Sdk_Availabilityinternal fix
+ */
+tSCC zDarwin_Nix_Sdk_AvailabilityinternalName[] =
+     "darwin_nix_sdk_availabilityinternal";
+
+/*
+ *  File name selection pattern
+ */
+tSCC zDarwin_Nix_Sdk_AvailabilityinternalList[] =
+  "AvailabilityInternal.h\0";
+/*
+ *  Machine/OS name selection pattern
+ */
+tSCC* apzDarwin_Nix_Sdk_AvailabilityinternalMachs[] = {
+        "*-*-darwin*",
+        (const char*)NULL };
+
+/*
+ *  content selection pattern - do fix if pattern found
+ */
+tSCC zDarwin_Nix_Sdk_AvailabilityinternalSelect0[] =
+       "(.*)__has_builtin\\(__is_target_os\\)(.*)";
+
+#define    DARWIN_NIX_SDK_AVAILABILITYINTERNAL_TEST_CT  1
+static tTestDesc aDarwin_Nix_Sdk_AvailabilityinternalTests[] = {
+  { TT_EGREP,    zDarwin_Nix_Sdk_AvailabilityinternalSelect0, (regex_t*)NULL }, };
+
+/*
+ *  Fix Command Arguments for Darwin_Nix_Sdk_Availabilityinternal
+ */
+static const char* apzDarwin_Nix_Sdk_AvailabilityinternalPatch[] = {
+    "format",
+    "%10%2",
+    (char*)NULL };
+
 /* * * * * * * * * * * * * * * * * * * * * * * * * *
  *
  *  Description of Dec_Intern_Asm fix
@@ -10445,9 +10482,9 @@ static const char* apzX11_SprintfPatch[] = {
  *
  *  List of all fixes
  */
-#define REGEX_COUNT          296
+#define REGEX_COUNT          297
 #define MACH_LIST_SIZE_LIMIT 187
-#define FIX_COUNT            257
+#define FIX_COUNT            258
 
 /*
  *  Enumerate the fixes
@@ -10535,6 +10572,7 @@ typedef enum {
     DARWIN_STDINT_6_FIXIDX,
     DARWIN_STDINT_7_FIXIDX,
     DARWIN_UCRED__ATOMIC_FIXIDX,
+    DARWIN_NIX_SDK_AVAILABILITYINTERNAL_FIXIDX,
     DEC_INTERN_ASM_FIXIDX,
     DJGPP_WCHAR_H_FIXIDX,
     ECD_CURSOR_FIXIDX,
@@ -11123,6 +11161,11 @@ tFixDesc fixDescList[ FIX_COUNT ] = {
      DARWIN_UCRED__ATOMIC_TEST_CT, FD_MACH_ONLY | FD_SUBROUTINE,
      aDarwin_Ucred__AtomicTests,   apzDarwin_Ucred__AtomicPatch, 0 },
 
+  {  zDarwin_Nix_Sdk_AvailabilityinternalName,    zDarwin_Nix_Sdk_AvailabilityinternalList,
+     apzDarwin_Nix_Sdk_AvailabilityinternalMachs,
+     DARWIN_NIX_SDK_AVAILABILITYINTERNAL_TEST_CT, FD_MACH_ONLY | FD_SUBROUTINE,
+     aDarwin_Nix_Sdk_AvailabilityinternalTests,   apzDarwin_Nix_Sdk_AvailabilityinternalPatch, 0 },
+
   {  zDec_Intern_AsmName,    zDec_Intern_AsmList,
      apzDec_Intern_AsmMachs,
      DEC_INTERN_ASM_TEST_CT, FD_MACH_ONLY,
diff --git a/fixincludes/inclhack.def b/fixincludes/inclhack.def
index bf136fdaa20..89bceb46c26 100644
--- a/fixincludes/inclhack.def
+++ b/fixincludes/inclhack.def
@@ -1727,6 +1727,20 @@ fix = {
     test_text = ""; /* Don't provide this for wrap fixes.  */
 };
 
+/*
+ * Newer versions of AvailabilityInternal.h use `__has_builtin`,
+ * which is not implemented in or compatible with GCC.
+ */
+fix = {
+    hackname  = darwin_nix_sdk_availabilityinternal;
+    mach      = "*-*-darwin*";
+    files     = AvailabilityInternal.h;
+    c_fix     = format;
+    c_fix_arg = "%10%2";
+    select    = "(.*)__has_builtin\\(__is_target_os\\)(.*)";
+    test_text = "__has_builtin(__is_target_os)";
+};
+
 /*
  *  Fix <c_asm.h> on Digital UNIX V4.0:
  *  It contains a prototype for a DEC C internal asm() function,