diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -542,9 +542,6 @@
 
 def err_drv_invalid_object_mode : Error<"OBJECT_MODE setting %0 is not recognized and is not a valid setting.">;
 
-def err_aix_default_altivec_abi : Error<
-  "The default Altivec ABI on AIX is not yet supported, use '-mabi=vec-extabi' for the extended Altivec ABI">;
-
 def err_aix_unsupported_tls_model : Error<"TLS model '%0' is not yet supported on AIX">;
 
 def err_invalid_cxx_abi : Error<"Invalid C++ ABI name '%0'">;
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -4823,7 +4823,7 @@
     if (A->getOption().getID() == options::OPT_mabi_EQ_vec_extabi)
       CmdArgs.push_back("-mabi=vec-extabi");
     else
-      D.Diag(diag::err_aix_default_altivec_abi);
+      CmdArgs.push_back("-mabi=vec-default");
   }
 
   if (Arg *A = Args.getLastArg(options::OPT_Wframe_larger_than_EQ)) {
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1859,13 +1859,7 @@
           << A->getSpelling() << T.str();
 
     const Option &O = A->getOption();
-    if (O.matches(OPT_mabi_EQ_vec_default))
-      Diags.Report(diag::err_aix_default_altivec_abi)
-          << A->getSpelling() << T.str();
-    else {
-      assert(O.matches(OPT_mabi_EQ_vec_extabi));
-      Opts.EnableAIXExtendedAltivecABI = 1;
-    }
+    Opts.EnableAIXExtendedAltivecABI = O.matches(OPT_mabi_EQ_vec_extabi);
   }
 
   bool NeedLocTracking = false;
diff --git a/clang/test/CodeGen/altivec.c b/clang/test/CodeGen/altivec.c
--- a/clang/test/CodeGen/altivec.c
+++ b/clang/test/CodeGen/altivec.c
@@ -4,12 +4,12 @@
 // RUN: %clang_cc1 -target-feature +altivec -triple powerpc64le-unknown-unknown -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-LE
 // RUN: %clang_cc1 -target-feature +altivec -mabi=vec-extabi -target-cpu pwr8 -triple powerpc-unknown-aix -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
 // RUN: %clang_cc1 -target-feature +altivec -mabi=vec-extabi -target-cpu pwr8 -triple powerpc64-unknown-aix -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
-// RUN: not %clang_cc1 -target-feature +altivec -mabi=vec-default -target-cpu pwr8 -triple powerpc-unknown-aix -emit-llvm %s 2>&1 | FileCheck %s --check-prefix=AIX-ERROR
-// RUN: not %clang_cc1 -target-feature +altivec -mabi=vec-default -target-cpu pwr8 -triple powerpc64-unknown-aix -emit-llvm %s 2>&1 | FileCheck %s --check-prefix=AIX-ERROR
-// RUN: %clang -S -emit-llvm -maltivec -mabi=vec-extabi -mcpu=pwr8 -target powerpc-unknown-aix %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
-// RUN: %clang -S -emit-llvm -maltivec -mabi=vec-extabi -mcpu=pwr8 -target powerpc64-unknown-aix %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
-// RUN: not %clang -S -emit-llvm -maltivec -mabi=vec-default -mcpu=pwr8 -triple powerpc-unknown-aix -emit-llvm %s 2>&1 | FileCheck %s --check-prefix=AIX-ERROR
-// RUN: not %clang -S -emit-llvm -maltivec -mabi=vec-default -mcpu=pwr8 -triple powerpc64-unknown-aix -emit-llvm %s 2>&1 | FileCheck %s --check-prefix=AIX-ERROR
+// RUN: %clang_cc1 -target-feature +altivec -mabi=vec-default -target-cpu pwr8 -triple powerpc-unknown-aix -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
+// RUN: %clang_cc1 -target-feature +altivec -mabi=vec-default -target-cpu pwr8 -triple powerpc64-unknown-aix -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
+// RUN: %clang -S -emit-llvm -maltivec -mabi=vec-extabi -mcpu=pwr8 --target=powerpc-unknown-aix %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
+// RUN: %clang -S -emit-llvm -maltivec -mabi=vec-extabi -mcpu=pwr8 --target=powerpc64-unknown-aix %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
+// RUN: %clang -S -emit-llvm -maltivec -mabi=vec-default -mcpu=pwr8 --target=powerpc-unknown-aix -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
+// RUN: %clang -S -emit-llvm -maltivec -mabi=vec-default -mcpu=pwr8 --target=powerpc64-unknown-aix -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-BE
 // Check initialization
 
 vector int test0 = (vector int)(1);       // CHECK: @test0 ={{.*}} global <4 x i32> <i32 1, i32 1, i32 1, i32 1>
@@ -52,5 +52,3 @@
   vector float vf;
   vf++;                                    // CHECK: fadd <4 x float> {{.*}} <float 1.000000e+{{0+}}, float 1.000000e+{{0+}}, float 1.000000e+{{0+}}, float 1.000000e+{{0+}}>
 }
-
-// AIX-ERROR:  error: The default Altivec ABI on AIX is not yet supported, use '-mabi=vec-extabi' for the extended Altivec ABI
diff --git a/clang/test/Driver/aix-vec-extabi.c b/clang/test/Driver/aix-vec-extabi.c
--- a/clang/test/Driver/aix-vec-extabi.c
+++ b/clang/test/Driver/aix-vec-extabi.c
@@ -1,10 +1,10 @@
 // RUN:  %clang -### -target powerpc-unknown-aix -S -maltivec -mabi=vec-extabi %s 2>&1 | \
-// RUN:  FileCheck %s
-
-// CHECK: "-cc1"
-// CHECK-SAME: "-mabi=vec-extabi"
-
+// RUN:  FileCheck %s --check-prefix=EXTABI
 // RUN:  %clang -### -target powerpc-unknown-aix -S -maltivec -mabi=vec-default %s 2>&1 | \
-// RUN:  FileCheck %s --check-prefix=ERROR
+// RUN:  FileCheck %s --check-prefix=DFLTABI
+
+// EXTABI:       "-cc1"
+// EXTABI-SAME:  "-mabi=vec-extabi"
 
-// ERROR: The default Altivec ABI on AIX is not yet supported, use '-mabi=vec-extabi' for the extended Altivec ABI
+// DFLTABI:      "-cc1"
+// DFLTABI-SAME: "-mabi=vec-default"
diff --git a/clang/test/Preprocessor/aix-vec_extabi.c b/clang/test/Preprocessor/aix-vec_extabi.c
--- a/clang/test/Preprocessor/aix-vec_extabi.c
+++ b/clang/test/Preprocessor/aix-vec_extabi.c
@@ -2,11 +2,11 @@
 // RUN:   | FileCheck %s -check-prefix=EXTABI
 // RUN: %clang  -target powerpc64-ibm-aix-xcoff -mcpu=pwr8 -E -dM -maltivec -mabi=vec-extabi %s -o - 2>&1 \
 // RUN:   | FileCheck %s -check-prefix=EXTABI
-// RUN: not %clang  -target powerpc-ibm-aix-xcoff -mcpu=pwr8 -E -dM -maltivec -mabi=vec-default %s 2>&1 \
+// RUN: %clang  -target powerpc-ibm-aix-xcoff -mcpu=pwr8 -E -dM -maltivec -mabi=vec-default %s 2>&1 \
 // RUN:   | FileCheck %s -check-prefix=DFLTABI
-// RUN: not %clang -target powerpc64-ibm-aix-xcoff -mcpu=pwr8 -E -dM -maltivec -mabi=vec-default %s 2>&1 \
+// RUN: %clang -target powerpc64-ibm-aix-xcoff -mcpu=pwr8 -E -dM -maltivec -mabi=vec-default %s 2>&1 \
 // RUN:   | FileCheck %s -check-prefix=DFLTABI
 
 
-// EXTABI:  #define __EXTABI__
-// DFLTABI: The default Altivec ABI on AIX is not yet supported, use '-mabi=vec-extabi' for the extended Altivec ABI
+// EXTABI:      #define __EXTABI__
+// DFLTABI-NOT: #define __EXTABI__