diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2986,6 +2986,8 @@
   "redeclaration has different alignment requirement (%1 vs %0)">;
 def err_alignas_underaligned : Error<
   "requested alignment is less than minimum alignment of %1 for type %0">;
+def warn_aligned_attr_underaligned : Warning<err_alignas_underaligned.Text>,
+  InGroup<IgnoredAttributes>;
 def err_attribute_sizeless_type : Error<
   "%0 attribute cannot be applied to sizeless type %1">;
 def err_attribute_argument_n_type : Error<
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -4063,12 +4063,12 @@
     return;
   }
 
-  if (Context.getTargetInfo().isTLSSupported()) {
+  const auto *VD = dyn_cast<VarDecl>(D);
+  if (VD && Context.getTargetInfo().isTLSSupported()) {
     unsigned MaxTLSAlign =
         Context.toCharUnitsFromBits(Context.getTargetInfo().getMaxTLSAlign())
             .getQuantity();
-    const auto *VD = dyn_cast<VarDecl>(D);
-    if (MaxTLSAlign && AlignVal > MaxTLSAlign && VD &&
+    if (MaxTLSAlign && AlignVal > MaxTLSAlign &&
         VD->getTLSKind() != VarDecl::TLS_None) {
       Diag(VD->getLocation(), diag::err_tls_var_aligned_over_maximum)
           << (unsigned)AlignVal << VD << MaxTLSAlign;
@@ -4076,6 +4076,17 @@
     }
   }
 
+  // On AIX, an aligned attribute can not decrease the alignment when applied
+  // to a variable declaration with vector type.
+  if (VD && Context.getTargetInfo().getTriple().isOSAIX()) {
+    const Type *Ty = VD->getType().getTypePtr();
+    if (Ty->isVectorType() && AlignVal < 16) {
+      Diag(VD->getLocation(), diag::warn_aligned_attr_underaligned)
+          << VD->getType() << 16;
+      return;
+    }
+  }
+
   AlignedAttr *AA = ::new (Context) AlignedAttr(Context, CI, true, ICE.get());
   AA->setPackExpansion(IsPackExpansion);
   D->addAttr(AA);
diff --git a/clang/test/CodeGen/aix-vector-attr-aligned.c b/clang/test/CodeGen/aix-vector-attr-aligned.c
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/aix-vector-attr-aligned.c
@@ -0,0 +1,33 @@
+// REQUIRES: powerpc-registered-target
+// RUN: %clang_cc1 -triple powerpc-unknown-aix -target-feature +altivec -target-cpu pwr7 -emit-llvm -o - %s | \
+// RUN:   FileCheck %s
+// RUN: %clang_cc1 -triple powerpc64-unknown-aix -target-feature +altivec -target-cpu pwr7 -emit-llvm -o - %s | \
+// RUN:   FileCheck %s
+
+typedef vector int __attribute__((aligned(8))) UnderAlignedVI;
+
+vector int g32 __attribute__((aligned(32)));
+vector int g8 __attribute__((aligned(8)));
+UnderAlignedVI TypedefedGlobal;
+
+int escape(vector int*);
+
+int local32(void) {
+  vector int l32 __attribute__((aligned(32)));
+  return escape(&l32);
+}
+
+int local8(void) {
+  vector int l8 __attribute__((aligned(8)));
+  return escape(&l8);
+}
+
+// CHECK: @g32 = global <4 x i32> zeroinitializer, align 32
+// CHECK: @g8 = global <4 x i32> zeroinitializer, align 16
+// CHECK: @TypedefedGlobal = global <4 x i32> zeroinitializer, align 8
+
+// CHECK-LABEL: @local32
+// CHECK:         %l32 = alloca <4 x i32>, align 32
+//
+// CHECK-LABEL: @local8
+// CHECK:         %l8 = alloca <4 x i32>, align 16
diff --git a/clang/test/Sema/aix-attr-aligned-vector-warn.c b/clang/test/Sema/aix-attr-aligned-vector-warn.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Sema/aix-attr-aligned-vector-warn.c
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -triple powerpc64-unknown-aix -target-feature +altivec -target-cpu pwr7 -verify -fsyntax-only %s
+// RUN: %clang_cc1 -triple powerpc-unknown-aix -target-feature +altivec -target-cpu pwr7 -verify -fsyntax-only %s
+
+int escape(vector int*);
+
+typedef vector int __attribute__((aligned(8))) UnderAlignedVI;
+UnderAlignedVI TypedefedGlobal;
+
+vector int V __attribute__((aligned(8))); // expected-warning {{requested alignment is less than minimum alignment of 16 for type '__vector int' (vector of 4 'int' values)}}
+
+int localTypedefed(void) {
+  UnderAlignedVI TypedefedLocal;
+  return escape(&TypedefedLocal); // expected-warning {{passing 8-byte aligned argument to 16-byte aligned parameter 1 of 'escape' may result in an unaligned pointer access}}
+}