diff --git a/clang-tools-extra/docs/ModularizeUsage.rst b/clang-tools-extra/docs/ModularizeUsage.rst
index dc335431ba74..6ac5d53d0bd9 100644
--- a/clang-tools-extra/docs/ModularizeUsage.rst
+++ b/clang-tools-extra/docs/ModularizeUsage.rst
@@ -49,3 +49,10 @@ Modularize Command Line Options
 
   Put modules generated by the -module-map-path option in an enclosing
   module with the given name.  See the description in :ref:`module-map-generation`.
+
+.. option:: -block-check-header-list-only
+
+  Limit the #include-inside-extern-or-namespace-block
+  check to only those headers explicitly listed in the header list.
+  This is a work-around for avoiding error messages for private includes that
+  purposefully get included inside blocks.
diff --git a/clang-tools-extra/modularize/Modularize.cpp b/clang-tools-extra/modularize/Modularize.cpp
index 49b2de045b1a..3504b75560b0 100644
--- a/clang-tools-extra/modularize/Modularize.cpp
+++ b/clang-tools-extra/modularize/Modularize.cpp
@@ -209,6 +209,15 @@ cl::opt<std::string>
 RootModule("root-module", cl::init(""),
            cl::desc("Specify the name of the root module."));
 
+// Option for limiting the #include-inside-extern-or-namespace-block
+// check to only those headers explicitly listed in the header list.
+// This is a work-around for private includes that purposefully get
+// included inside blocks.
+static cl::opt<bool>
+BlockCheckHeaderListOnly("block-check-header-list-only", cl::init(false),
+cl::desc("Only warn if #include directives are inside extern or namespace"
+  " blocks if the included header is in the header list."));
+
 // Save the program name for error messages.
 const char *Argv0;
 // Save the command line for comments.
@@ -722,7 +731,8 @@ int main(int Argc, const char **Argv) {
       new FixedCompilationDatabase(Twine(PathBuf), CC1Arguments));
 
   // Create preprocessor tracker, to watch for macro and conditional problems.
-  std::unique_ptr<PreprocessorTracker> PPTracker(PreprocessorTracker::create());
+  std::unique_ptr<PreprocessorTracker> PPTracker(
+    PreprocessorTracker::create(Headers, BlockCheckHeaderListOnly));
 
   // Parse all of the headers, detecting duplicates.
   EntityMap Entities;
diff --git a/clang-tools-extra/modularize/PreprocessorTracker.cpp b/clang-tools-extra/modularize/PreprocessorTracker.cpp
index 685e242032c7..2a41921cb463 100644
--- a/clang-tools-extra/modularize/PreprocessorTracker.cpp
+++ b/clang-tools-extra/modularize/PreprocessorTracker.cpp
@@ -866,9 +866,19 @@ ConditionalExpansionMapIter;
 // course of running modularize.
 class PreprocessorTrackerImpl : public PreprocessorTracker {
 public:
-  PreprocessorTrackerImpl()
-      : CurrentInclusionPathHandle(InclusionPathHandleInvalid),
-        InNestedHeader(false) {}
+  PreprocessorTrackerImpl(llvm::SmallVector<std::string, 32> &Headers,
+        bool DoBlockCheckHeaderListOnly)
+      : BlockCheckHeaderListOnly(DoBlockCheckHeaderListOnly),
+        CurrentInclusionPathHandle(InclusionPathHandleInvalid),
+        InNestedHeader(false) {
+    // Use canonical header path representation.
+    for (llvm::ArrayRef<std::string>::iterator I = Headers.begin(),
+      E = Headers.end();
+      I != E; ++I) {
+      HeaderList.push_back(getCanonicalPath(*I));
+    }
+  }
+
   ~PreprocessorTrackerImpl() {}
 
   // Handle entering a preprocessing session.
@@ -889,6 +899,10 @@ public:
   // "namespace {}" blocks containing #include directives.
   void handleIncludeDirective(llvm::StringRef DirectivePath, int DirectiveLine,
                               int DirectiveColumn, llvm::StringRef TargetPath) {
+    // If it's not a header in the header list, ignore it with respect to
+    // the check.
+    if (BlockCheckHeaderListOnly && !isHeaderListHeader(DirectivePath))
+      return;
     HeaderHandle CurrentHeaderHandle = findHeaderHandle(DirectivePath);
     StringHandle IncludeHeaderHandle = addString(TargetPath);
     for (std::vector<PPItemKey>::const_iterator I = IncludeDirectives.begin(),
@@ -959,6 +973,7 @@ public:
     if (!InNestedHeader)
       InNestedHeader = !HeadersInThisCompile.insert(H).second;
   }
+
   // Handle exiting a header source file.
   void handleHeaderExit(llvm::StringRef HeaderPath) {
     // Ignore <built-in> and <command-line> to reduce message clutter.
@@ -982,6 +997,18 @@ public:
     return CanonicalPath;
   }
 
+  // Return true if the given header is in the header list.
+  bool isHeaderListHeader(llvm::StringRef HeaderPath) const {
+    std::string CanonicalPath = getCanonicalPath(HeaderPath);
+    for (llvm::ArrayRef<std::string>::iterator I = HeaderList.begin(),
+        E = HeaderList.end();
+        I != E; ++I) {
+      if (*I == CanonicalPath)
+        return true;
+    }
+    return false;
+  }
+
   // Get the handle of a header file entry.
   // Return HeaderHandleInvalid if not found.
   HeaderHandle findHeaderHandle(llvm::StringRef HeaderPath) const {
@@ -1301,6 +1328,9 @@ public:
   }
 
 private:
+  llvm::SmallVector<std::string, 32> HeaderList;
+  // Only do extern, namespace check for headers in HeaderList.
+  bool BlockCheckHeaderListOnly;
   llvm::StringPool Strings;
   std::vector<StringHandle> HeaderPaths;
   std::vector<HeaderHandle> HeaderStack;
@@ -1319,8 +1349,10 @@ private:
 PreprocessorTracker::~PreprocessorTracker() {}
 
 // Create instance of PreprocessorTracker.
-PreprocessorTracker *PreprocessorTracker::create() {
-  return new PreprocessorTrackerImpl();
+PreprocessorTracker *PreprocessorTracker::create(
+    llvm::SmallVector<std::string, 32> &Headers,
+    bool DoBlockCheckHeaderListOnly) {
+  return new PreprocessorTrackerImpl(Headers, DoBlockCheckHeaderListOnly);
 }
 
 // Preprocessor callbacks for modularize.
diff --git a/clang-tools-extra/modularize/PreprocessorTracker.h b/clang-tools-extra/modularize/PreprocessorTracker.h
index 4f72d0146317..a283d9f2f8f3 100644
--- a/clang-tools-extra/modularize/PreprocessorTracker.h
+++ b/clang-tools-extra/modularize/PreprocessorTracker.h
@@ -77,7 +77,9 @@ public:
   virtual bool reportInconsistentConditionals(llvm::raw_ostream &OS) = 0;
 
   // Create instance of PreprocessorTracker.
-  static PreprocessorTracker *create();
+  static PreprocessorTracker *create(
+    llvm::SmallVector<std::string, 32> &Headers,
+    bool DoBlockCheckHeaderListOnly);
 };
 
 } // end namespace Modularize
diff --git a/clang-tools-extra/test/modularize/NoProblemsNamespace.modularize b/clang-tools-extra/test/modularize/NoProblemsNamespace.modularize
new file mode 100644
index 000000000000..1c3f78d069a5
--- /dev/null
+++ b/clang-tools-extra/test/modularize/NoProblemsNamespace.modularize
@@ -0,0 +1,3 @@
+# RUN: modularize -block-check-header-list-only
+
+Inputs/IncludeInNamespace.h