diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
index 085fb52..032a20a 100644
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -448,8 +448,8 @@
   return nullptr;
 }
 
-StringRef getRealizedPlatform(const AvailabilityAttr *A,
-                              const ASTContext &Context) {
+static StringRef getRealizedPlatform(const AvailabilityAttr *A,
+                                     const ASTContext &Context) {
   // Check if this is an App Extension "platform", and if so chop off
   // the suffix for matching with the actual platform.
   StringRef RealizedPlatform = A->getPlatform()->getName();