Index: test/Index/print-type-size.c
===================================================================
--- /dev/null
+++ test/Index/print-type-size.c
@@ -0,0 +1,30 @@
+struct Foo {
+    int size;
+    void* data[]; // incomplete array
+};
+
+struct Bar {
+    int size;
+    struct {
+        int dummy;
+        void* data[]; // incomplete array
+    };
+};
+
+struct Baz {
+    int size;
+    union {
+        void* data1[]; // incomplete array
+        void* data2[]; // incomplete array
+    };
+};
+
+// RUN: c-index-test -test-print-type-size %s | FileCheck %s
+// CHECK: FieldDecl=size:2:9 (Definition) [type=int] [typekind=Int] [sizeof=4] [alignof=4] [offsetof=0]
+// CHECK: FieldDecl=data:3:11 (Definition) [type=void *[]] [typekind=IncompleteArray] [sizeof=-2] [alignof=8] [offsetof=64]
+// CHECK: FieldDecl=size:7:9 (Definition) [type=int] [typekind=Int] [sizeof=4] [alignof=4] [offsetof=0]
+// CHECK: FieldDecl=dummy:9:13 (Definition) [type=int] [typekind=Int] [sizeof=4] [alignof=4] [offsetof=64/0]
+// CHECK: FieldDecl=data:10:15 (Definition) [type=void *[]] [typekind=IncompleteArray] [sizeof=-2] [alignof=8] [offsetof=128/64]
+// CHECK: FieldDecl=size:15:9 (Definition) [type=int] [typekind=Int] [sizeof=4] [alignof=4] [offsetof=0]
+// CHECK: FieldDecl=data1:17:15 (Definition) [type=void *[]] [typekind=IncompleteArray] [sizeof=-2] [alignof=8] [offsetof=64/0]
+// CHECK: FieldDecl=data2:18:15 (Definition) [type=void *[]] [typekind=IncompleteArray] [sizeof=-2] [alignof=8] [offsetof=64/0]
\ No newline at end of file
Index: tools/libclang/CXType.cpp
===================================================================
--- tools/libclang/CXType.cpp
+++ tools/libclang/CXType.cpp
@@ -895,7 +895,7 @@
   // [expr.alignof] p3: if reference type, return size of referenced type
   if (QT->isReferenceType())
     QT = QT.getNonReferenceType();
-  if (QT->isIncompleteType())
+  if (QT->isIncompleteType() && !QT->isIncompleteArrayType()) // IAT is okay here
     return CXTypeLayoutError_Incomplete;
   if (QT->isDependentType())
     return CXTypeLayoutError_Dependent;
@@ -953,7 +953,7 @@
 static long long visitRecordForValidation(const RecordDecl *RD) {
   for (const auto *I : RD->fields()){
     QualType FQT = I->getType();
-    if (FQT->isIncompleteType())
+    if (FQT->isIncompleteType() && !FQT->isIncompleteArrayType()) // IAT is okay here
       return CXTypeLayoutError_Incomplete;
     if (FQT->isDependentType())
       return CXTypeLayoutError_Dependent;