diff --git a/clang/include/clang/Basic/SourceManager.h b/clang/include/clang/Basic/SourceManager.h
--- a/clang/include/clang/Basic/SourceManager.h
+++ b/clang/include/clang/Basic/SourceManager.h
@@ -95,9 +95,6 @@
   /// This object owns the MemoryBuffer object.
   class alignas(8) ContentCache {
     enum CCFlags {
-      /// Whether the buffer is invalid.
-      InvalidFlag = 0x01,
-
       /// Whether the buffer should not be freed on destruction.
       DoNotFreeFlag = 0x02
     };
@@ -151,18 +148,21 @@
     /// after serialization and deserialization.
     unsigned IsTransient : 1;
 
+    mutable unsigned IsBufferInvalid : 1;
+
     ContentCache(const FileEntry *Ent = nullptr) : ContentCache(Ent, Ent) {}
 
     ContentCache(const FileEntry *Ent, const FileEntry *contentEnt)
         : Buffer(nullptr, false), OrigEntry(Ent), ContentsEntry(contentEnt),
-          BufferOverridden(false), IsFileVolatile(false), IsTransient(false) {}
+          BufferOverridden(false), IsFileVolatile(false), IsTransient(false),
+          IsBufferInvalid(false) {}
 
     /// The copy ctor does not allow copies where source object has either
     /// a non-NULL Buffer or SourceLineCache.  Ownership of allocated memory
     /// is not transferred, so this is a logical error.
     ContentCache(const ContentCache &RHS)
         : Buffer(nullptr, false), BufferOverridden(false),
-          IsFileVolatile(false), IsTransient(false) {
+          IsFileVolatile(false), IsTransient(false), IsBufferInvalid(false) {
       OrigEntry = RHS.OrigEntry;
       ContentsEntry = RHS.ContentsEntry;
 
@@ -216,11 +216,6 @@
     /// with the given buffer.
     void replaceBuffer(const llvm::MemoryBuffer *B, bool DoNotFree = false);
 
-    /// Determine whether the buffer itself is invalid.
-    bool isBufferInvalid() const {
-      return Buffer.getInt() & InvalidFlag;
-    }
-
     /// Determine whether the buffer should be freed.
     bool shouldFreeBuffer() const {
       return (Buffer.getInt() & DoNotFreeFlag) == 0;
diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -123,7 +123,7 @@
                               SourceLocation Loc) const {
   // Lazily create the Buffer for ContentCaches that wrap files.  If we already
   // computed it, just return what we have.
-  if (isBufferInvalid())
+  if (IsBufferInvalid)
     return None;
   if (auto *B = Buffer.getPointer())
     return B->getMemBufferRef();
@@ -144,7 +144,7 @@
       Diag.Report(Loc, diag::err_file_too_large)
         << ContentsEntry->getName();
 
-    Buffer.setInt(Buffer.getInt() | InvalidFlag);
+    IsBufferInvalid = true;
     return None;
   }
 
@@ -164,7 +164,7 @@
       Diag.Report(Loc, diag::err_cannot_open_file)
           << ContentsEntry->getName() << BufferOrError.getError().message();
 
-    Buffer.setInt(Buffer.getInt() | InvalidFlag);
+    IsBufferInvalid = true;
     return None;
   }
 
@@ -180,7 +180,7 @@
       Diag.Report(Loc, diag::err_file_modified)
         << ContentsEntry->getName();
 
-    Buffer.setInt(Buffer.getInt() | InvalidFlag);
+    IsBufferInvalid = true;
     return None;
   }
 
@@ -193,7 +193,7 @@
   if (InvalidBOM) {
     Diag.Report(Loc, diag::err_unsupported_bom)
       << InvalidBOM << ContentsEntry->getName();
-    Buffer.setInt(Buffer.getInt() | InvalidFlag);
+    IsBufferInvalid = true;
     return None;
   }