diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 832aee2..fc97981 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -1288,6 +1288,9 @@
     bool needsImportVisitation() const override { return true; }
 
     void visitImport(StringRef FileName) override {
+      if (!CI.ExplicitlyLoadedModuleFiles.insert(FileName).second)
+        return;
+
       ModuleFileStack.push_back(FileName);
       if (ASTReader::readASTFileControlBlock(FileName, CI.getFileManager(),
                                              *this)) {