Index: lib/AST/ExprClassification.cpp
===================================================================
--- lib/AST/ExprClassification.cpp
+++ lib/AST/ExprClassification.cpp
@@ -643,6 +643,14 @@
     if (R->hasConstFields())
       return Cl::CM_ConstQualifiedField;
 
+  if (const ExtVectorElementExpr *VE = dyn_cast<ExtVectorElementExpr>(E))
+    if (Ctx.getCanonicalType(VE->getBase()->getType()).isConstQualified())
+      return Cl::CM_ConstQualified;
+
+  if (const ArraySubscriptExpr *ASE = dyn_cast<ArraySubscriptExpr>(E))
+    if (Ctx.getCanonicalType(ASE->getBase()->getType()).isConstQualified())
+      return Cl::CM_ConstQualified;
+
   return Cl::CM_Modifiable;
 }
 
Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp
+++ lib/Sema/SemaExpr.cpp
@@ -10321,7 +10321,7 @@
 /// 'const' due to being captured within a block?
 enum NonConstCaptureKind { NCCK_None, NCCK_Block, NCCK_Lambda };
 static NonConstCaptureKind isReferenceToNonConstCapture(Sema &S, Expr *E) {
-  assert(E->isLValue() && E->getType().isConstQualified());
+  assert(E->isLValue());
   E = E->IgnoreParens();
 
   // Must be a reference to a declaration from an enclosing scope.
Index: test/SemaCXX/err_typecheck_assign_const.cpp
===================================================================
--- test/SemaCXX/err_typecheck_assign_const.cpp
+++ test/SemaCXX/err_typecheck_assign_const.cpp
@@ -129,3 +129,21 @@
   Func &bar();
   bar()() = 0; // expected-error {{read-only variable is not assignable}}
 }
+
+typedef float float4 __attribute__((ext_vector_type(4)));
+struct OhNo {
+  float4 v;
+  void AssignMe() const { v.x = 1; } // expected-error {{read-only variable is not assignable}}
+};
+
+typedef float float4_2 __attribute__((__vector_size__(16)));
+struct OhNo2 {
+  float4_2 v;
+  void AssignMe() const { v[0] = 1; } // expected-error {{read-only variable is not assignable}}
+};
+
+struct OhNo3 {
+  float v[4];
+  void AssignMe() const { v[0] = 1; } // expected-error {{read-only variable is not assignable}}
+};
+