diff --git a/src/subsidy_func.h b/src/subsidy_func.h
--- a/src/subsidy_func.h
+++ b/src/subsidy_func.h
@@ -20,7 +20,6 @@
 Pair SetupSubsidyDecodeParam(const struct Subsidy *s, bool mode);
 void DeleteSubsidyWith(SourceType type, SourceID index);
 bool CheckSubsidised(CargoID cargo_type, CompanyID company, SourceType src_type, SourceID src, const Station *st);
-void SubsidyMonthlyHandler();
 void RebuildSubsidisedSourceAndDestinationCache();
 void DeleteSubsidy(struct Subsidy *s);