diff --git a/src/json-validator.cpp b/src/json-validator.cpp
index 91b7e22..fbcb9ed 100644
--- a/src/json-validator.cpp
+++ b/src/json-validator.cpp
@@ -10,6 +10,7 @@
 
 #include <memory>
 #include <set>
+#include <sstream>
 
 using nlohmann::json;
 using nlohmann::json_uri;