diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 807a855..b14317e 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1518,6 +1518,15 @@
   "cast between pointer-to-function and pointer-to-object is an extension">;
 def err_bad_reinterpret_cast_small_int : Error<
   "cast from pointer to smaller type %2 loses information">;
+def err_bad_cxx_cast_vector_to_scalar_different_size : Error<
+  "%select{||reinterpret_cast||C-style cast|}0 from vector %1 " 
+  "to scalar %2 of different size">;
+def err_bad_cxx_cast_scalar_to_vector_different_size : Error<
+  "%select{||reinterpret_cast||C-style cast|}0 from scalar %1 " 
+  "to vector %2 of different size">;
+def err_bad_cxx_cast_vector_to_vector_different_size : Error<
+  "%select{||reinterpret_cast||C-style cast|}0 from vector %1 " 
+  "to vector %2 of different size">;
 def err_bad_lvalue_to_rvalue_cast : Error<
   "cannot cast from lvalue of type %1 to rvalue reference type %2; types are "
   "not compatible">;
diff --git a/lib/Sema/SemaCXXCast.cpp b/lib/Sema/SemaCXXCast.cpp
index dbd6c6f..f0ae9a1 100644
--- a/lib/Sema/SemaCXXCast.cpp
+++ b/lib/Sema/SemaCXXCast.cpp
@@ -956,6 +956,32 @@
     return TC_Success;
   }
 
+  bool destIsVector = DestType->isVectorType();
+  bool srcIsVector = SrcType->isVectorType();
+  if (srcIsVector || destIsVector) {
+    bool srcIsScalar = SrcType->isIntegralType() && !SrcType->isEnumeralType();
+    bool destIsScalar = 
+      DestType->isIntegralType() && !DestType->isEnumeralType();
+    
+    // Check if this is a cast between a vector and something else.
+    if (!(srcIsScalar && destIsVector) && !(srcIsVector && destIsScalar) &&
+        !(srcIsVector && destIsVector))
+      return TC_NotApplicable;
+
+    // If both types have the same size, we can successfully cast.
+    if (Self.Context.getTypeSize(SrcType) == Self.Context.getTypeSize(DestType))
+      return TC_Success;
+    
+    if (destIsScalar)
+      msg = diag::err_bad_cxx_cast_vector_to_scalar_different_size;
+    else if (srcIsScalar)
+      msg = diag::err_bad_cxx_cast_scalar_to_vector_different_size;
+    else
+      msg = diag::err_bad_cxx_cast_vector_to_vector_different_size;
+    
+    return TC_Failed;
+  }
+  
   bool destIsPtr = DestType->isPointerType();
   bool srcIsPtr = SrcType->isPointerType();
   if (!destIsPtr && !srcIsPtr) {
diff --git a/test/SemaCXX/vector-casts.cpp b/test/SemaCXX/vector-casts.cpp
new file mode 100644
index 0000000..5b08043
--- /dev/null
+++ b/test/SemaCXX/vector-casts.cpp
@@ -0,0 +1,40 @@
+// RUN: clang-cc -fsyntax-only -verify %s
+typedef int __v2si __attribute__((__vector_size__(8)));
+typedef short __v4hi __attribute__((__vector_size__(8)));
+typedef short __v8hi __attribute__((__vector_size__(16)));
+
+struct S { };
+
+void f() {
+  __v2si v2si;
+  __v4hi v4hi;
+  __v8hi v8hi;
+  unsigned long long ll;
+  unsigned char c;
+  S s;
+  
+  (void)reinterpret_cast<__v2si>(v4hi);
+  (void)(__v2si)v4hi;
+  (void)reinterpret_cast<__v4hi>(v2si);
+  (void)(__v4hi)v2si;
+  (void)reinterpret_cast<unsigned long long>(v2si);
+  (void)(unsigned long long)v2si;
+  (void)reinterpret_cast<__v2si>(ll);
+  (void)(__v2si)(ll);
+
+  (void)reinterpret_cast<S>(v2si); // expected-error {{reinterpret_cast from '__v2si' to 'struct S' is not allowed}}
+  (void)(S)v2si; // expected-error {{C-style cast from '__v2si' to 'struct S' is not allowed}}
+  (void)reinterpret_cast<__v2si>(s); // expected-error {{reinterpret_cast from 'struct S' to '__v2si' is not allowed}}
+  (void)(__v2si)s; // expected-error {{C-style cast from 'struct S' to '__v2si' is not allowed}}
+  
+  (void)reinterpret_cast<unsigned char>(v2si); // expected-error {{reinterpret_cast from vector '__v2si' to scalar 'unsigned char' of different size}}
+  (void)(unsigned char)v2si; // expected-error {{C-style cast from vector '__v2si' to scalar 'unsigned char' of different size}}
+  (void)reinterpret_cast<__v2si>(c); // expected-error {{reinterpret_cast from scalar 'unsigned char' to vector '__v2si' of different size}}
+
+  (void)reinterpret_cast<__v8hi>(v4hi); // expected-error {{reinterpret_cast from vector '__v4hi' to vector '__v8hi' of different size}}
+  (void)(__v8hi)v4hi; // expected-error {{C-style cast from vector '__v4hi' to vector '__v8hi' of different size}}
+  (void)reinterpret_cast<__v4hi>(v8hi); // expected-error {{reinterpret_cast from vector '__v8hi' to vector '__v4hi' of different size}}
+  (void)(__v4hi)v8hi; // expected-error {{C-style cast from vector '__v8hi' to vector '__v4hi' of different size}}
+}
+
+