Index: lib/CodeGen/CGDecl.cpp
===================================================================
--- lib/CodeGen/CGDecl.cpp
+++ lib/CodeGen/CGDecl.cpp
@@ -1848,9 +1848,12 @@
   // Use better IR generation for certain implicit parameters.
   if (auto IPD = dyn_cast<ImplicitParamDecl>(&D)) {
     // The only implicit argument a block has is its literal.
-    // We assume this is always passed directly.
+    // This may be passed as an inalloca'ed value on Windows x86.
     if (BlockInfo) {
-      setBlockContextParameter(IPD, ArgNo, Arg.getDirectValue());
+      llvm::Value *V = Arg.isIndirect()
+                           ? Builder.CreateLoad(Arg.getIndirectAddress())
+                           : Arg.getDirectValue();
+      setBlockContextParameter(IPD, ArgNo, V);
       return;
     }
   }
Index: test/CodeGenCXX/block-inalloca.cpp
===================================================================
--- /dev/null
+++ test/CodeGenCXX/block-inalloca.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -triple i686-unknown-windows-msvc -fblocks -emit-llvm -o - %s | FileCheck %s
+
+struct S {
+  S(const struct S &) {}
+};
+
+void (^b)(S) = ^(S) {};
+
+// CHECK: [[DESCRIPTOR:%.*]] = getelementptr inbounds <{ i8*, %struct.S, [3 x i8] }>, <{ i8*, %struct.S, [3 x i8] }>* %0, i32 0, i32 0
+// CHECK: load i8*, i8** [[DESCRIPTOR]]
+