diff --git a/clang/lib/CodeGen/CodeGenTypes.cpp b/clang/lib/CodeGen/CodeGenTypes.cpp
index ee629ec9b0de..87b3da50005b 100644
--- a/clang/lib/CodeGen/CodeGenTypes.cpp
+++ b/clang/lib/CodeGen/CodeGenTypes.cpp
@@ -419,6 +419,14 @@ llvm::Type *CodeGenTypes::ConvertType(QualType T) {
   case Type::ConstantArray: {
     const ConstantArrayType *A = cast<ConstantArrayType>(Ty);
     llvm::Type *EltTy = ConvertTypeForMem(A->getElementType());
+    
+    // Lower arrays of undefined struct type to arrays of i8 just to have a 
+    // concrete type.
+    if (!EltTy->isSized()) {
+      SkippedLayout = true;
+      EltTy = llvm::Type::getInt8Ty(getLLVMContext());
+    }
+
     ResultType = llvm::ArrayType::get(EltTy, A->getSize().getZExtValue());
     break;
   }
diff --git a/clang/test/CodeGenCXX/incomplete-types.cpp b/clang/test/CodeGenCXX/incomplete-types.cpp
index 4f37eeb97549..1d4f430e5cb5 100644
--- a/clang/test/CodeGenCXX/incomplete-types.cpp
+++ b/clang/test/CodeGenCXX/incomplete-types.cpp
@@ -35,3 +35,9 @@ namespace PR10395 {
   extern T x[];
   T* f() { return x; }
 }
+
+namespace PR10384 {
+  struct X;
+  extern X x[1];
+  X* f() { return x; }
+}