diff --git a/protos_generator/gen_utils.h b/protos_generator/gen_utils.h
index 5563f9f..394c244 100644
--- a/protos_generator/gen_utils.h
+++ b/protos_generator/gen_utils.h
@@ -28,6 +28,8 @@
 #ifndef UPB_PROTOS_GENERATOR_GEN_UTILS_H_
 #define UPB_PROTOS_GENERATOR_GEN_UTILS_H_
 
+#include <vector>
+
 #include "google/protobuf/descriptor.pb.h"
 #include "absl/container/flat_hash_map.h"
 #include "absl/strings/string_view.h"
@@ -88,6 +90,8 @@
 
 inline constexpr absl::string_view kNoPackageNamePrefix = "protos_";
 
+std::string ToCamelCase(const std::string& input, bool lower_first);
+
 }  // namespace protos_generator
 
 #endif  // UPB_PROTOS_GENERATOR_GEN_UTILS_H_