diff --git a/toolchain/driver/compile_subcommand.cpp b/toolchain/driver/compile_subcommand.cpp
index 6a913da62db2..9f53b25d9783 100644
--- a/toolchain/driver/compile_subcommand.cpp
+++ b/toolchain/driver/compile_subcommand.cpp
@@ -5,6 +5,7 @@
 #include "toolchain/driver/compile_subcommand.h"
 
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/Support/Path.h"
 #include "toolchain/diagnostics/emitter.h"
 #include "toolchain/diagnostics/format_providers.h"