diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 0565a7f..b4c375d 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -7118,6 +7118,13 @@
       switch (KeyFunction->getTemplateSpecializationKind()) {
       case TSK_Undeclared:
       case TSK_ExplicitSpecialization:
+        // The key function is in another translation unit. Mark all of the
+        // virtual members of this class as referenced so that we can build a
+        // vtable anyway (in order to do devirtualization when optimizations
+        // are turned on for example.
+        MarkVirtualMembersReferenced(Loc, Class);
+        continue;
+
       case TSK_ExplicitInstantiationDeclaration:
         // The key function is in another translation unit.
         continue;