diff --git a/llvm/tools/llvm-mt/llvm-mt.cpp b/llvm/tools/llvm-mt/llvm-mt.cpp
--- a/llvm/tools/llvm-mt/llvm-mt.cpp
+++ b/llvm/tools/llvm-mt/llvm-mt.cpp
@@ -150,9 +150,11 @@
     bool Same = false;
     if (OutBuffOrErr) {
       const std::unique_ptr<MemoryBuffer> &FileBuffer = *OutBuffOrErr;
-      Same = std::equal(OutputBuffer->getBufferStart(),
-                        OutputBuffer->getBufferEnd(),
-                        FileBuffer->getBufferStart());
+      bool SameSize =
+          OutputBuffer->getBufferSize() == FileBuffer->getBufferSize();
+      Same = SameSize && std::equal(OutputBuffer->getBufferStart(),
+                                    OutputBuffer->getBufferEnd(),
+                                    FileBuffer->getBufferStart());
     }
     if (!Same) {
 #if LLVM_ON_UNIX