diff --git a/lib/library.cpp b/lib/library.cpp
index bd4a62d0a42..efba862eb15 100644
--- a/lib/library.cpp
+++ b/lib/library.cpp
@@ -123,9 +123,9 @@ struct Library::LibraryData
     std::map<std::string, AllocFunc> mDealloc; // deallocation functions
     std::map<std::string, AllocFunc> mRealloc; // reallocation functions
     std::unordered_map<std::string, FalseTrueMaybe> mNoReturn; // is function noreturn?
-    std::map<std::string, std::string> mReturnValue;
-    std::map<std::string, std::string> mReturnValueType;
-    std::map<std::string, int> mReturnValueContainer;
+    std::unordered_map<std::string, std::string> mReturnValue;
+    std::unordered_map<std::string, std::string> mReturnValueType;
+    std::unordered_map<std::string, int> mReturnValueContainer;
     std::map<std::string, std::vector<MathLib::bigint>> mUnknownReturnValues;
     std::map<std::string, bool> mReportErrors;
     std::map<std::string, bool> mProcessAfterCode;