Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -8219,6 +8219,8 @@
 def err_kernel_arg_address_space : Error<
   "pointer arguments to kernel functions must reside in '__global', "
   "'__constant' or '__local' address space">;
+def err_opencl_ext_vector_component_invalid_length : Error<
+  "vector component access has invalid length %0.  Supported: 1,2,3,4,8,16.">;
 def err_opencl_function_variable : Error<
   "%select{non-kernel function|function scope}0 variable cannot be declared in %1 address space">;
 def err_static_function_scope : Error<
Index: lib/Sema/SemaExprMember.cpp
===================================================================
--- lib/Sema/SemaExprMember.cpp
+++ lib/Sema/SemaExprMember.cpp
@@ -284,6 +284,16 @@
   }
 }
 
+// OpenCL spec (Section 6.1.7 Vector Components):
+// The component group notation can occur on the left hand side of an expression. To form an lvalue,
+// swizzling must be applied to an l-value of vector type, contain no duplicate components,
+// and it results in an l-value of scalar or vector type, depending on number of components
+// specified. Each component must be a supported scalar or vector type.
+static bool IsValidSwizzleLength(unsigned len)
+{
+  return (len >= 1 && len <= 4) || len == 8 || len == 16;
+}
+
 /// Check an ext-vector component access expression.
 ///
 /// VK should be set in advance to the value kind of the base
@@ -376,6 +386,20 @@
     }
   }
 
+  if (S.getLangOpts().OpenCL && !HalvingSwizzle) {
+    compStr = CompName->getNameStart();
+
+    if (HexSwizzle)
+      compStr++;
+
+    unsigned swizzleLength = StringRef(compStr).size();
+    if (IsValidSwizzleLength(swizzleLength) == false) {
+      S.Diag(OpLoc, diag::err_opencl_ext_vector_component_invalid_length)
+        << swizzleLength << SourceRange(CompLoc);
+      return QualType();
+    }
+  }
+
   // The component accessor looks fine - now we need to compute the actual type.
   // The vector type is implied by the component accessor. For example,
   // vec4.b is a float, vec4.xy is a vec2, vec4.rgb is a vec3, etc.
Index: test/SemaOpenCL/vector_swizzle_length.cl
===================================================================
--- /dev/null
+++ test/SemaOpenCL/vector_swizzle_length.cl
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 %s -verify -pedantic -fsyntax-only
+
+typedef float float8 __attribute__((ext_vector_type(8)));
+
+void foo() {
+    float8 f2 = (float8)(0, 0, 0, 0, 0, 0, 0, 0);
+
+    f2.s01234; // expected-error {{vector component access has invalid length 5.  Supported: 1,2,3,4,8,16}}
+}