diff --git a/common/error.h b/common/error.h
index be3361b328d3..403befc461dd 100644
--- a/common/error.h
+++ b/common/error.h
@@ -6,6 +6,7 @@
 #define CARBON_COMMON_ERROR_H_
 
 #include <string>
+#include <variant>
 
 #include "common/check.h"
 #include "common/ostream.h"