diff --git a/clang/include/clang/Frontend/PrecompiledPreamble.h b/clang/include/clang/Frontend/PrecompiledPreamble.h
index 5ae77735576cdf..0d95ee683eee2c 100644
--- a/clang/include/clang/Frontend/PrecompiledPreamble.h
+++ b/clang/include/clang/Frontend/PrecompiledPreamble.h
@@ -38,7 +38,7 @@ class PCHContainerOperations;
 
 /// Runs lexer to compute suggested preamble bounds.
 PreambleBounds ComputePreambleBounds(const LangOptions &LangOpts,
-                                     llvm::MemoryBuffer *Buffer,
+                                     const llvm::MemoryBuffer *Buffer,
                                      unsigned MaxLines);
 
 class PreambleCallbacks;
diff --git a/clang/lib/Frontend/PrecompiledPreamble.cpp b/clang/lib/Frontend/PrecompiledPreamble.cpp
index 3657ccf8eceab3..442ad63cee0e48 100644
--- a/clang/lib/Frontend/PrecompiledPreamble.cpp
+++ b/clang/lib/Frontend/PrecompiledPreamble.cpp
@@ -228,7 +228,7 @@ template <class T> bool moveOnNoError(llvm::ErrorOr<T> Val, T &Output) {
 } // namespace
 
 PreambleBounds clang::ComputePreambleBounds(const LangOptions &LangOpts,
-                                            llvm::MemoryBuffer *Buffer,
+                                            const llvm::MemoryBuffer *Buffer,
                                             unsigned MaxLines) {
   return Lexer::ComputePreamble(Buffer->getBuffer(), LangOpts, MaxLines);
 }