diff --git a/clang/lib/CodeGen/CGRTTI.cpp b/clang/lib/CodeGen/CGRTTI.cpp
index d1b370a..b5cdd7f 100644
--- a/clang/lib/CodeGen/CGRTTI.cpp
+++ b/clang/lib/CodeGen/CGRTTI.cpp
@@ -779,28 +779,24 @@
     cast<CXXRecordDecl>(Base->getType()->getAs<RecordType>()->getDecl());
   
   if (Base->isVirtual()) {
-    if (Bases.VirtualBases.count(BaseDecl)) {
+    // Mark the virtual base as seen.
+    if (!Bases.VirtualBases.insert(BaseDecl)) {
       // If this virtual base has been seen before, then the class is diamond
       // shaped.
       Flags |= RTTIBuilder::VMI_DiamondShaped;
     } else {
       if (Bases.NonVirtualBases.count(BaseDecl))
         Flags |= RTTIBuilder::VMI_NonDiamondRepeat;
-
-      // Mark the virtual base as seen.
-      Bases.VirtualBases.insert(BaseDecl);
     }
   } else {
-    if (Bases.NonVirtualBases.count(BaseDecl)) {
+    // Mark the non-virtual base as seen.
+    if (!Bases.NonVirtualBases.insert(BaseDecl)) {
       // If this non-virtual base has been seen before, then the class has non-
       // diamond shaped repeated inheritance.
       Flags |= RTTIBuilder::VMI_NonDiamondRepeat;
     } else {
       if (Bases.VirtualBases.count(BaseDecl))
         Flags |= RTTIBuilder::VMI_NonDiamondRepeat;
-        
-      // Mark the non-virtual base as seen.
-      Bases.NonVirtualBases.insert(BaseDecl);
     }
   }