diff --git a/clang/include/clang/AST/UnresolvedSet.h b/clang/include/clang/AST/UnresolvedSet.h
--- a/clang/include/clang/AST/UnresolvedSet.h
+++ b/clang/include/clang/AST/UnresolvedSet.h
@@ -121,7 +121,7 @@
   void setAccess(iterator I, AccessSpecifier AS) { I.I->setAccess(AS); }
 
   void clear() { decls().clear(); }
-  void set_size(unsigned N) { decls().set_size(N); }
+  void truncate(unsigned N) { decls().truncate(N); }
 
   bool empty() const { return decls().empty(); }
   unsigned size() const { return decls().size(); }
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -620,7 +620,7 @@
     getSema().diagnoseEquivalentInternalLinkageDeclarations(
         getNameLoc(), HasNonFunction, EquivalentNonFunctions);
 
-  Decls.set_size(N);
+  Decls.truncate(N);
 
   if (HasNonFunction && (HasFunction || HasUnresolved))
     Ambiguous = true;