diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -653,11 +653,7 @@
     // Check whether we know anything about this macro name or not.
     llvm::StringMap<std::pair<StringRef, bool /*IsUndef*/>>::iterator Known =
         ASTFileMacros.find(MacroName);
-    if (!Validate || Known == ASTFileMacros.end()) {
-      // FIXME: Check whether this identifier was referenced anywhere in the
-      // AST file. If so, we should reject the AST file. Unfortunately, this
-      // information isn't in the control block. What shall we do about it?
-
+    if (!Validate) {
       if (Existing.second) {
         SuggestedPredefines += "#undef ";
         SuggestedPredefines += MacroName.str();
@@ -671,6 +667,12 @@
       }
       continue;
     }
+    if (Known == ASTFileMacros.end()) {
+      if (Diags) {
+        Diags->Report(diag::err_pch_macro_def_undef) << MacroName << true;
+      }
+      return true;
+    }
 
     // If the macro was defined in one but undef'd in the other, we have a
     // conflict.
@@ -684,8 +686,10 @@
 
     // If the macro was #undef'd in both, or if the macro bodies are identical,
     // it's fine.
-    if (Existing.second || Existing.first == Known->second.first)
+    if (Existing.second || Existing.first == Known->second.first) {
+      ASTFileMacros.erase(Known);
       continue;
+    }
 
     // The macro bodies differ; complain.
     if (Diags) {
@@ -694,6 +698,12 @@
     }
     return true;
   }
+  for (const auto &MacroName : ASTFileMacros.keys()) {
+    if (Diags) {
+      Diags->Report(diag::err_pch_macro_def_undef) << MacroName << false;
+    }
+    return true;
+  }
 
   // Check whether we're using predefines.
   if (PPOpts.UsePredefines != ExistingPPOpts.UsePredefines && Validate) {
@@ -5171,7 +5181,7 @@
     bool ReadPreprocessorOptions(const PreprocessorOptions &PPOpts,
                                  bool Complain,
                                  std::string &SuggestedPredefines) override {
-      return checkPreprocessorOptions(ExistingPPOpts, PPOpts, nullptr, FileMgr,
+      return checkPreprocessorOptions(PPOpts, ExistingPPOpts, nullptr, FileMgr,
                                       SuggestedPredefines, ExistingLangOpts);
     }
   };
diff --git a/clang/test/PCH/fuzzy-pch.c b/clang/test/PCH/fuzzy-pch.c
--- a/clang/test/PCH/fuzzy-pch.c
+++ b/clang/test/PCH/fuzzy-pch.c
@@ -1,7 +1,9 @@
 // Test with pch.
 // RUN: %clang_cc1 -emit-pch -DFOO -o %t %S/variables.h
-// RUN: %clang_cc1 -DBAR=int -include-pch %t -fsyntax-only -pedantic %s
-// RUN: %clang_cc1 -DFOO -DBAR=int -include-pch %t %s
+// RUN: not %clang_cc1 -DBAR=int -include-pch %t -fsyntax-only -pedantic %s 2> %t.err
+// RUN: FileCheck -check-prefix=CHECK-BAR %s < %t.err
+// RUN: not %clang_cc1 -DFOO -DBAR=int -include-pch %t %s 2> %t.err
+// RUN: FileCheck -check-prefix=CHECK-BAR %s < %t.err
 // RUN: not %clang_cc1 -DFOO=blah -DBAR=int -include-pch %t %s 2> %t.err
 // RUN: FileCheck -check-prefix=CHECK-FOO %s < %t.err
 // RUN: not %clang_cc1 -UFOO -include-pch %t %s 2> %t.err
@@ -26,6 +28,7 @@
 
 // CHECK-FOO: definition of macro 'FOO' differs between the precompiled header ('1') and the command line ('blah')
 // CHECK-NOFOO: macro 'FOO' was defined in the precompiled header but undef'd on the command line
+// CHECK-BAR: macro 'BAR' was undef'd in the precompiled header but defined on the command line
 
 // CHECK-UNDEF: command line contains '-undef' but precompiled header was not built with it
 
diff --git a/clang/test/PCH/pch-dir.c b/clang/test/PCH/pch-dir.c
--- a/clang/test/PCH/pch-dir.c
+++ b/clang/test/PCH/pch-dir.c
@@ -6,7 +6,7 @@
 // RUN: %clang -x c++-header -std=c++98 %S/pch-dir.h -o %t.h.gch/cpp.gch 
 // RUN: %clang -include %t.h -DFOO=foo -fsyntax-only %s -Xclang -print-stats 2> %t.clog
 // RUN: FileCheck -check-prefix=CHECK-C %s < %t.clog
-// RUN: %clang -include %t.h -DFOO=bar -DBAR=bar -fsyntax-only %s -Xclang -ast-print > %t.cbarlog
+// RUN: %clang -include %t.h -DFOO=bar -fsyntax-only %s -Xclang -ast-print > %t.cbarlog
 // RUN: FileCheck -check-prefix=CHECK-CBAR %s < %t.cbarlog
 // RUN: %clang -x c++ -include %t.h -std=c++98 -fsyntax-only %s -Xclang -print-stats 2> %t.cpplog
 // RUN: FileCheck -check-prefix=CHECK-CPP %s < %t.cpplog
@@ -14,6 +14,11 @@
 // RUN: not %clang -x c++ -std=c++11 -include %t.h -fsyntax-only %s 2> %t.cpp11log
 // RUN: FileCheck -check-prefix=CHECK-NO-SUITABLE %s < %t.cpp11log
 
+// RUN: not %clang -include %t.h -fsyntax-only %s 2> %t.missinglog2
+// RUN: FileCheck -check-prefix=CHECK-NO-SUITABLE %s < %t.missinglog2
+// RUN: not %clang -include %t.h -DFOO=foo -DBAR=bar -fsyntax-only %s 2> %t.missinglog2
+// RUN: FileCheck -check-prefix=CHECK-NO-SUITABLE %s < %t.missinglog2
+
 // Don't crash if the precompiled header file is missing.
 // RUN: not %clang_cc1 -include-pch %t.h.gch -DFOO=baz -fsyntax-only %s -print-stats 2> %t.missinglog
 // RUN: FileCheck -check-prefix=CHECK-NO-SUITABLE %s < %t.missinglog