diff --git a/lib/Basic/Targets.cpp b/lib/Basic/Targets.cpp
index 8ff30d9..7f30ac5 100644
--- a/lib/Basic/Targets.cpp
+++ b/lib/Basic/Targets.cpp
@@ -3079,11 +3079,12 @@ bool X86TargetInfo::validateOperandSize(StringRef Constraint,
   default: break;
   case 'y':
     return Size <= 64;
-  case 'x':
   case 'f':
   case 't':
   case 'u':
     return Size <= 128;
+  case 'x':
+    return Size <= 256;
   }
 
   return true;
diff --git a/test/CodeGen/x86_32-inline-asm.c b/test/CodeGen/x86_32-inline-asm.c
index 18fe4d0..288ac4d 100644
--- a/test/CodeGen/x86_32-inline-asm.c
+++ b/test/CodeGen/x86_32-inline-asm.c
@@ -43,6 +43,7 @@ int func1() {
   __asm__ volatile("foo1 %0" : : "f" (val256)); // expected-error {{invalid input size for constraint 'f'}}
   __asm__ volatile("foo1 %0" : : "t" (val256)); // expected-error {{invalid input size for constraint 't'}}
   __asm__ volatile("foo1 %0" : : "u" (val256)); // expected-error {{invalid input size for constraint 'u'}}
+  __asm__ volatile("foo1 %0" : : "x" (val256)); // No error.
 
   __asm__ volatile("foo1 %0" : "=R" (val)); // expected-error {{invalid output size for constraint '=R'}}
   __asm__ volatile("foo1 %0" : "=q" (val)); // expected-error {{invalid output size for constraint '=q'}}
@@ -56,4 +57,5 @@ int func1() {
   __asm__ volatile("foo1 %0" : "=A" (val128)); // expected-error {{invalid output size for constraint '=A'}}
   __asm__ volatile("foo1 %0" : "=t" (val256)); // expected-error {{invalid output size for constraint '=t'}}
   __asm__ volatile("foo1 %0" : "=u" (val256)); // expected-error {{invalid output size for constraint '=u'}}
+  __asm__ volatile("foo1 %0" : "=x" (val256)); // No error.
 }