diff --git a/src/campaign_server/campaign_server.cpp b/src/campaign_server/campaign_server.cpp
index 3f3f091ad36..2e8a6973ba7 100644
--- a/src/campaign_server/campaign_server.cpp
+++ b/src/campaign_server/campaign_server.cpp
@@ -930,3 +930,6 @@ int main()
 
 	return 0;
 }
+
+void deprecated_message(const std::string&, int, const version_info&, const std::string&);
+void deprecated_message(const std::string&, int, const version_info&, const std::string&) {}
diff --git a/src/formula/formula.cpp b/src/formula/formula.cpp
index 1b441a5fc37..a2819573c74 100644
--- a/src/formula/formula.cpp
+++ b/src/formula/formula.cpp
@@ -33,6 +33,8 @@ static lg::log_domain log_engine("engine");
 
 namespace utils {
 	namespace detail {
+		std::string evaluate_formula_impl(const std::string&);
+
 		std::string evaluate_formula_impl(const std::string& formula) {
 			try {
 				const wfl::formula form(formula);
diff --git a/src/server/server.cpp b/src/server/server.cpp
index 5c2e94151b3..44e6e66c783 100644
--- a/src/server/server.cpp
+++ b/src/server/server.cpp
@@ -2832,3 +2832,6 @@ int main(int argc, char** argv) {
 
 	return 0;
 }
+
+void deprecated_message(const std::string&, int, const version_info&, const std::string&);
+void deprecated_message(const std::string&, int, const version_info&, const std::string&) {}