Index: lib/Sema/SemaCodeComplete.cpp
===================================================================
--- lib/Sema/SemaCodeComplete.cpp
+++ lib/Sema/SemaCodeComplete.cpp
@@ -5061,7 +5061,20 @@
   if (SS.isInvalid()) {
     CodeCompletionContext CC(CodeCompletionContext::CCC_Symbol);
     CC.setCXXScopeSpecifier(SS);
-    HandleCodeCompleteResults(this, CodeCompleter, CC, nullptr, 0);
+    // As SS is invalid, we try to collect accessible contexts from the current
+    // scope with a dummy lookup so that the completion consumer can try to
+    // guess what the specified scope is.
+    ResultBuilder DummyResults(*this, CodeCompleter->getAllocator(),
+                               CodeCompleter->getCodeCompletionTUInfo(), CC);
+    if (S->getEntity()) {
+      CodeCompletionDeclConsumer Consumer(DummyResults, S->getEntity(),
+                                          BaseType);
+      LookupVisibleDecls(S, LookupOrdinaryName, Consumer,
+                         /*IncludeGlobalScope=*/false,
+                         /*LoadExternal=*/false);
+    }
+    HandleCodeCompleteResults(this, CodeCompleter,
+                              DummyResults.getCompletionContext(), nullptr, 0);
     return;
   }
   // Always pretend to enter a context to ensure that a dependent type
Index: unittests/Sema/CodeCompleteTest.cpp
===================================================================
--- unittests/Sema/CodeCompleteTest.cpp
+++ unittests/Sema/CodeCompleteTest.cpp
@@ -181,6 +181,18 @@
   EXPECT_TRUE(VisitedNS.empty());
 }
 
+TEST(SemaCodeCompleteTest, VisitedNSForInvalidQualifiedId) {
+  auto VisitedNS = runCodeCompleteOnCode(R"cpp(
+     namespace na {}
+     namespace ns1 {
+     using namespace na;
+     foo::^
+     }
+  )cpp")
+                       .VisitedNamespaces;
+  EXPECT_THAT(VisitedNS, UnorderedElementsAre("ns1::", "na::"));
+}
+
 TEST(SemaCodeCompleteTest, VisitedNSWithoutQualifier) {
   auto VisitedNS = runCodeCompleteOnCode(R"cpp(
     namespace n1 {