diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 83319a808787..c65db7e835ed 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -4954,6 +4954,7 @@ Sema::CheckTransparentUnionArgumentConstraints(QualType ArgType, Expr *&rExpr) {
 
     if (CheckAssignmentConstraints(it->getType(), rExpr->getType())
           == Compatible) {
+      ImpCastExprToType(rExpr, it->getType(), CK_Unknown);
       InitField = *it;
       break;
     }
diff --git a/clang/test/CodeGen/transparent-union.c b/clang/test/CodeGen/transparent-union.c
new file mode 100644
index 000000000000..9f1cdda18d10
--- /dev/null
+++ b/clang/test/CodeGen/transparent-union.c
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -triple i386-unknown-unknown -emit-llvm -o %t %s
+// RUN: FileCheck < %t %s
+//
+// FIXME: Note that we don't currently get the ABI right here. f0() should be
+// f0(i8*).
+
+typedef union {
+  void *f0;
+} transp_t0 __attribute__((transparent_union));
+
+void f0(transp_t0 obj);
+
+// CHECK: define void @f1_0(i32* %a0) 
+// CHECK:  call void @f0(%union.anon* byval %{{.*}})
+// CHECK: }
+void f1_0(int *a0) {
+  f0(a0);
+}
+
+void f1_1(int *a0) {
+  f0((transp_t0) { a0 });
+}