diff --git a/llvm/lib/Support/CommandLine.cpp b/llvm/lib/Support/CommandLine.cpp
index 920811a..012f759 100644
--- a/llvm/lib/Support/CommandLine.cpp
+++ b/llvm/lib/Support/CommandLine.cpp
@@ -24,6 +24,7 @@
 #include <algorithm>
 #include <functional>
 #include <map>
+#include <ostream>
 #include <set>
 #include <cstdlib>
 #include <cerrno>