diff --git a/internal/core/src/segcore/Reduce.h b/internal/core/src/segcore/Reduce.h
index 0930489864..ee4df168f6 100644
--- a/internal/core/src/segcore/Reduce.h
+++ b/internal/core/src/segcore/Reduce.h
@@ -16,6 +16,7 @@
 #include <memory>
 #include <vector>
 #include <queue>
+#include <unordered_set>
 
 #include "utils/Status.h"
 #include "common/type_c.h"
diff --git a/internal/core/src/segcore/ReduceStructure.h b/internal/core/src/segcore/ReduceStructure.h
index 1f25091965..e1b2813092 100644
--- a/internal/core/src/segcore/ReduceStructure.h
+++ b/internal/core/src/segcore/ReduceStructure.h
@@ -60,4 +60,4 @@ struct SearchResultPairComparator {
     operator()(const SearchResultPair* lhs, const SearchResultPair* rhs) const {
         return *lhs > *rhs;
     }
-};
\ No newline at end of file
+};