diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 80543fd..834041c 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -8428,6 +8428,13 @@
   if (FD) {
     FD->setBody(Body);
 
+    // The only way to be included in UndefinedInternals is if there is an
+    // ODR-use before the definition. Avoid the expensive map lookup if this
+    // is the first declaration.
+    if (FD->getPreviousDecl() != 0 && FD->getPreviousDecl()->isUsed() &&
+        FD->getLinkage() != ExternalLinkage)
+      UndefinedInternals.erase(FD);
+
     // If the function implicitly returns zero (like 'main') or is naked,
     // don't complain about missing return statements.
     if (FD->hasImplicitReturnZero() || FD->hasAttr<NakedAttr>())