diff --git a/lib/Sema/TreeTransform.h b/lib/Sema/TreeTransform.h
index db5e2d1..05ae38e 100644
--- a/lib/Sema/TreeTransform.h
+++ b/lib/Sema/TreeTransform.h
@@ -6279,6 +6279,10 @@
   if (!ND)
     return SemaRef.ExprError();
   
+  // Is this instantiation of a __block variable?
+  if (E->getDecl()->getAttr<BlocksAttr>())
+    ND->addAttr(::new (SemaRef.Context) BlocksAttr(BlocksAttr::ByRef));
+  
   if (!getDerived().AlwaysRebuild() &&
       ND == E->getDecl()) {
     // Mark it referenced in the new context regardless.
diff --git a/test/CodeGenCXX/instantiate-blocks.cpp b/test/CodeGenCXX/instantiate-blocks.cpp
index 8c1c8dd..7246f69 100644
--- a/test/CodeGenCXX/instantiate-blocks.cpp
+++ b/test/CodeGenCXX/instantiate-blocks.cpp
@@ -18,7 +18,11 @@
 template <typename T, typename T1> void foo(T t, T1 r)
 {
     T block_arg;
-    T1 (^block)(char, T, T1, double) =  ^ T1 (char ch, T arg, T1 arg2, double d1) { return block_arg+arg; };
+    __block T1 byref_block_arg;
+
+    T1 (^block)(char, T, T1, double) =  
+	^ T1 (char ch, T arg, T1 arg2, double d1) { byref_block_arg = arg2;
+           					    return byref_block_arg + arg; };
 
     void (^block2)() = ^{};
 }
diff --git a/test/SemaCXX/instantiate-blocks.cpp b/test/SemaCXX/instantiate-blocks.cpp
new file mode 100644
index 0000000..a4001a7
--- /dev/null
+++ b/test/SemaCXX/instantiate-blocks.cpp
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -fblocks -fsyntax-only -verify %s
+// rdar: // 6182276
+
+template <typename T, typename T1> void foo(T t, T1 r)
+{
+    T block_arg;
+    __block T1 byref_block_arg;
+
+    T1 (^block)(T)  =  ^ T1 (T arg) { 
+         byref_block_arg = arg;
+         block_arg = arg; 	// expected-error {{variable is not assignable (missing __block type specifier)}}
+         return block_arg+arg; };
+}
+
+int main(void)
+{
+    foo(100, 'a');	// expected-note {{in instantiation of function template specialization 'foo<int, char>' requested here}}
+}
+