diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index c2ff2238d5fd..f9f6cee994ec 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -1590,6 +1590,7 @@ QualType Sema::BuildArrayType(QualType T, ArrayType::ArraySizeModifier ASM,
       // Prohibit the use of non-POD types in VLAs.
       QualType BaseT = Context.getBaseElementType(T);
       if (!T->isDependentType() &&
+          !RequireCompleteType(Loc, BaseT, 0) &&
           !BaseT.isPODType(Context) &&
           !BaseT->isObjCLifetimeType()) {
         Diag(Loc, diag::err_vla_non_pod)
diff --git a/clang/test/SemaCXX/vla.cpp b/clang/test/SemaCXX/vla.cpp
index d63b6335f453..dae6450553aa 100644
--- a/clang/test/SemaCXX/vla.cpp
+++ b/clang/test/SemaCXX/vla.cpp
@@ -3,3 +3,17 @@
 // PR11925
 int n;
 int (&f())[n]; // expected-error {{function declaration cannot have variably modified type}}
+
+namespace PR18581 {
+  template<typename T> struct pod {};
+  template<typename T> struct error {
+    typename T::error e; // expected-error {{cannot be used prior to '::'}}
+  };
+  struct incomplete; // expected-note {{forward declaration}}
+
+  void f(int n) {
+    pod<int> a[n];
+    error<int> b[n]; // expected-note {{instantiation}}
+    incomplete c[n]; // expected-error {{incomplete}}
+  }
+}