Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6461,6 +6461,8 @@
   "ordered comparison between pointer and zero (%0 and %1)">;
 def err_typecheck_three_way_comparison_of_pointer_and_zero : Error<
   "three-way comparison between pointer and zero">;
+def err_typecheck_comparison_of_complete_and_incomplete_types : Error<
+  "ordered comparison of complete and incomplete pointers (%0 and %1)">;
 def ext_typecheck_ordered_comparison_of_function_pointers : ExtWarn<
   "ordered comparison of function pointers (%0 and %1)">,
   InGroup<DiagGroup<"ordered-compare-function-pointers">>;
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -11426,8 +11426,15 @@
     // C99 6.5.9p2 and C99 6.5.8p2
     if (Context.typesAreCompatible(LCanPointeeTy.getUnqualifiedType(),
                                    RCanPointeeTy.getUnqualifiedType())) {
-      // Valid unless a relational comparison of function pointers
-      if (IsRelational && LCanPointeeTy->isFunctionType()) {
+      // Pointers both need to point to complete or incomplete types
+      if (LCanPointeeTy->isIncompleteType() !=
+          RCanPointeeTy->isIncompleteType()) {
+        Diag(Loc,
+             diag::err_typecheck_comparison_of_complete_and_incomplete_types)
+            << LHSType << RHSType << LHS.get()->getSourceRange()
+            << RHS.get()->getSourceRange();
+      } else if (IsRelational && LCanPointeeTy->isFunctionType()) {
+        // Valid unless a relational comparison of function pointers
         Diag(Loc, diag::ext_typecheck_ordered_comparison_of_function_pointers)
           << LHSType << RHSType << LHS.get()->getSourceRange()
           << RHS.get()->getSourceRange();
Index: clang/test/Sema/compare.c
===================================================================
--- clang/test/Sema/compare.c
+++ clang/test/Sema/compare.c
@@ -405,3 +405,12 @@
   if (x == y) x = y; // no warning
   if (y == x) y = x; // no warning
 }
+
+int incomplete[]; // expected-warning {{tentative array definition assumed to have one element}}
+int complete[5];
+
+void test13() {
+  if (&incomplete < &complete) { // expected-error {{ordered comparison of complete and incomplete pointers}}
+    return;
+  }
+}