diff --git a/llvm/lib/System/Unix/MappedFile.cpp b/llvm/lib/System/Unix/MappedFile.cpp
index 1c9622d..36a17e0 100644
--- a/llvm/lib/System/Unix/MappedFile.cpp
+++ b/llvm/lib/System/Unix/MappedFile.cpp
@@ -108,7 +108,7 @@
   return base_;
 }
 
-size_t MappedFile::size() {
+size_t MappedFile::size() const {
   assert(info_ && "MappedFile not initialized");
   return info_->sbuf_.st_size;
 }