diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -1578,11 +1578,26 @@
   return TheCall;
 }
 
+// Emit an error and return true if the current object format type is in the
+// list of unsupported types.
+static bool CheckBuiltinTargetNotInUnsupported(
+    Sema &S, unsigned BuiltinID, CallExpr *TheCall,
+    ArrayRef<llvm::Triple::ObjectFormatType> UnsupportedObjectFormatTypes) {
+  llvm::Triple::ObjectFormatType CurObjFormat =
+      S.getASTContext().getTargetInfo().getTriple().getObjectFormat();
+  if (llvm::is_contained(UnsupportedObjectFormatTypes, CurObjFormat)) {
+    S.Diag(TheCall->getBeginLoc(), diag::err_builtin_target_unsupported)
+        << TheCall->getSourceRange();
+    return true;
+  }
+  return false;
+}
+
 // Emit an error and return true if the current architecture is not in the list
 // of supported architectures.
 static bool
-CheckBuiltinTargetSupport(Sema &S, unsigned BuiltinID, CallExpr *TheCall,
-                          ArrayRef<llvm::Triple::ArchType> SupportedArchs) {
+CheckBuiltinTargetInSupported(Sema &S, unsigned BuiltinID, CallExpr *TheCall,
+                              ArrayRef<llvm::Triple::ArchType> SupportedArchs) {
   llvm::Triple::ArchType CurArch =
       S.getASTContext().getTargetInfo().getTriple().getArch();
   if (llvm::is_contained(SupportedArchs, CurArch))
@@ -1664,6 +1679,12 @@
 
   switch (BuiltinID) {
   case Builtin::BI__builtin___CFStringMakeConstantString:
+    // CFStringMakeConstantString is currently not implemented for GOFF (i.e.,
+    // on z/OS) and for XCOFF (i.e., on AIX). Emit unsupported
+    if (CheckBuiltinTargetNotInUnsupported(
+            *this, BuiltinID, TheCall,
+            {llvm::Triple::GOFF, llvm::Triple::XCOFF}))
+      return ExprError();
     assert(TheCall->getNumArgs() == 1 &&
            "Wrong # arguments to builtin CFStringMakeConstantString");
     if (CheckObjCString(TheCall->getArg(0)))
@@ -1698,7 +1719,7 @@
   case Builtin::BI_interlockedbittestandreset_acq:
   case Builtin::BI_interlockedbittestandreset_rel:
   case Builtin::BI_interlockedbittestandreset_nf:
-    if (CheckBuiltinTargetSupport(
+    if (CheckBuiltinTargetInSupported(
             *this, BuiltinID, TheCall,
             {llvm::Triple::arm, llvm::Triple::thumb, llvm::Triple::aarch64}))
       return ExprError();
@@ -1711,9 +1732,10 @@
   case Builtin::BI_bittestandset64:
   case Builtin::BI_interlockedbittestandreset64:
   case Builtin::BI_interlockedbittestandset64:
-    if (CheckBuiltinTargetSupport(*this, BuiltinID, TheCall,
-                                  {llvm::Triple::x86_64, llvm::Triple::arm,
-                                   llvm::Triple::thumb, llvm::Triple::aarch64}))
+    if (CheckBuiltinTargetInSupported(*this, BuiltinID, TheCall,
+                                      {llvm::Triple::x86_64, llvm::Triple::arm,
+                                       llvm::Triple::thumb,
+                                       llvm::Triple::aarch64}))
       return ExprError();
     break;
 
diff --git a/clang/test/Analysis/cfref_PR2519.c b/clang/test/Analysis/cfref_PR2519.c
--- a/clang/test/Analysis/cfref_PR2519.c
+++ b/clang/test/Analysis/cfref_PR2519.c
@@ -1,3 +1,4 @@
+// UNSUPPORTED: -zos, -aix
 // RUN: %clang_analyze_cc1 -analyzer-checker=core,osx.cocoa.RetainCount,alpha.core -analyzer-store=region -verify %s
 // expected-no-diagnostics
 
diff --git a/clang/test/CodeGen/cfstring2.c b/clang/test/CodeGen/cfstring2.c
--- a/clang/test/CodeGen/cfstring2.c
+++ b/clang/test/CodeGen/cfstring2.c
@@ -1,3 +1,4 @@
+// UNSUPPORTED: -zos, -aix
 // RUN: %clang_cc1 -emit-llvm %s -o %t
 
 typedef const struct __CFString * CFStringRef;
diff --git a/clang/test/Modules/builtins.m b/clang/test/Modules/builtins.m
--- a/clang/test/Modules/builtins.m
+++ b/clang/test/Modules/builtins.m
@@ -1,3 +1,4 @@
+// UNSUPPORTED: -zos, -aix
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fmodules-cache-path=%t -fmodules -fimplicit-module-maps -I %S/Inputs %s -verify
 // RUN: %clang_cc1 -fmodules-cache-path=%t -fmodules -fimplicit-module-maps -I %S/Inputs -x c %s -verify
diff --git a/clang/test/SemaCXX/builtins.cpp b/clang/test/SemaCXX/builtins.cpp
--- a/clang/test/SemaCXX/builtins.cpp
+++ b/clang/test/SemaCXX/builtins.cpp
@@ -4,7 +4,11 @@
 #define CFSTR __builtin___CFStringMakeConstantString
 
 void f() {
+#if !defined(__MVS__) && !defined(_AIX)
+  // Builtin function __builtin___CFStringMakeConstantString is currently
+  // unsupported on z/OS and AIX.
   (void)CFStringRef(CFSTR("Hello"));
+#endif
 }
 
 void a() { __builtin_va_list x, y; ::__builtin_va_copy(x, y); }