Index: include/clang/Lex/Preprocessor.h
===================================================================
--- include/clang/Lex/Preprocessor.h
+++ include/clang/Lex/Preprocessor.h
@@ -388,6 +388,7 @@
     SmallVector<PPConditionalInfo, 4> ConditionalStack;
     State ConditionalStackState = Off;
   } PreambleConditionalStack;
+  bool PreambleGenerationFailed = false;
 
   /// The current top of the stack that we're lexing from if
   /// not expanding a macro and we are lexing directly from source code.
@@ -2159,6 +2160,10 @@
                                                           Module *M,
                                                           SourceLocation MLoc);
 
+  bool preambleGenerationFailed() const {
+    return PreambleGenerationFailed;
+  }
+
   bool isRecordingPreamble() const {
     return PreambleConditionalStack.isRecording();
   }
Index: include/clang/Serialization/ASTWriter.h
===================================================================
--- include/clang/Serialization/ASTWriter.h
+++ include/clang/Serialization/ASTWriter.h
@@ -979,6 +979,7 @@
   ASTWriter &getWriter() { return Writer; }
   const ASTWriter &getWriter() const { return Writer; }
   SmallVectorImpl<char> &getPCH() const { return Buffer->Data; }
+  const Preprocessor &getPreprocessor() const { return PP; }
 
 public:
   PCHGenerator(const Preprocessor &PP, StringRef OutputFile, StringRef isysroot,
Index: lib/Frontend/PrecompiledPreamble.cpp
===================================================================
--- lib/Frontend/PrecompiledPreamble.cpp
+++ lib/Frontend/PrecompiledPreamble.cpp
@@ -170,6 +170,9 @@
   }
 
   void HandleTranslationUnit(ASTContext &Ctx) override {
+    if (getPreprocessor().preambleGenerationFailed())
+      return;
+
     PCHGenerator::HandleTranslationUnit(Ctx);
     if (!hasEmittedPCH())
       return;
Index: lib/Lex/PPDirectives.cpp
===================================================================
--- lib/Lex/PPDirectives.cpp
+++ lib/Lex/PPDirectives.cpp
@@ -1933,6 +1933,20 @@
     return;
   }
 
+  // Check whether it makes sense to continue preamble generation. We can't
+  // generate a consistent preamble with regard to the conditional stack if the
+  // main file is included again as due to the preamble bounds some directives
+  // (e.g. #endif of a header guard) will never be seen. Since this will lead to
+  // confusing errors, abort the preamble generation.
+  if (File && PreambleConditionalStack.isRecording() &&
+      SourceMgr.translateFile(File) == SourceMgr.getMainFileID()) {
+    PreambleGenerationFailed = true;
+    // Generate a fatal error to skip further processing.
+    Diag(FilenameTok.getLocation(), diag::err_pp_error_opening_file) << ""
+                                                                     << "";
+    return;
+  }
+
   // Should we enter the source file? Set to false if either the source file is
   // known to have no effect beyond its effect on module visibility -- that is,
   // if it's got an include guard that is already defined or is a modular header
Index: test/Index/preamble-cyclic-include.cpp
===================================================================
--- /dev/null
+++ test/Index/preamble-cyclic-include.cpp
@@ -0,0 +1,9 @@
+// RUN: env CINDEXTEST_EDITING=1 c-index-test -test-annotate-tokens=%s:4:1:8:1 %s 2>&1 | FileCheck %s
+// CHECK-NOT: error: unterminated conditional directive
+// CHECK-NOT: Skipping: [4:1 - 8:7]
+#ifndef A_H
+#define A_H
+#  include "preamble-cyclic-include.cpp"
+int bar();
+#endif
+