diff --git a/lib/library.cpp b/lib/library.cpp
index 154ab8ee2..be138e7a0 100644
--- a/lib/library.cpp
+++ b/lib/library.cpp
@@ -1414,7 +1414,7 @@ bool Library::isnoreturn(const Token *ftok) const
         return true;
     if (isNotLibraryFunction(ftok))
         return false;
-    const std::map<std::string, FalseTrueMaybe>::const_iterator it = mNoReturn.find(getFunctionName(ftok));
+    const std::unordered_map<std::string, FalseTrueMaybe>::const_iterator it = mNoReturn.find(getFunctionName(ftok));
     if (it == mNoReturn.end())
         return false;
     if (it->second == FalseTrueMaybe::Maybe)
@@ -1428,7 +1428,7 @@ bool Library::isnotnoreturn(const Token *ftok) const
         return false;
     if (isNotLibraryFunction(ftok))
         return false;
-    const std::map<std::string, FalseTrueMaybe>::const_iterator it = mNoReturn.find(getFunctionName(ftok));
+    const std::unordered_map<std::string, FalseTrueMaybe>::const_iterator it = mNoReturn.find(getFunctionName(ftok));
     if (it == mNoReturn.end())
         return false;
     if (it->second == FalseTrueMaybe::Maybe)
diff --git a/lib/library.h b/lib/library.h
index f8c983542..6456e3699 100644
--- a/lib/library.h
+++ b/lib/library.h
@@ -564,7 +564,7 @@ private:
     std::map<std::string, AllocFunc> mAlloc; // allocation functions
     std::map<std::string, AllocFunc> mDealloc; // deallocation functions
     std::map<std::string, AllocFunc> mRealloc; // reallocation functions
-    std::map<std::string, FalseTrueMaybe> mNoReturn; // is function noreturn?
+    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;
diff --git a/lib/tokenize.cpp b/lib/tokenize.cpp
index c611890f3..aa299cd3a 100644
--- a/lib/tokenize.cpp
+++ b/lib/tokenize.cpp
@@ -7381,7 +7381,7 @@ void Tokenizer::simplifyVariableMultipleAssign()
 }
 
 // Binary operators simplification map
-static const std::map<std::string, std::string> cAlternativeTokens = {
+static const std::unordered_map<std::string, std::string> cAlternativeTokens = {
     std::make_pair("and", "&&")
     , std::make_pair("and_eq", "&=")
     , std::make_pair("bitand", "&")
@@ -7437,7 +7437,7 @@ bool Tokenizer::simplifyCAlternativeTokens()
         if (!tok->isName())
             continue;
 
-        const std::map<std::string, std::string>::const_iterator cOpIt = cAlternativeTokens.find(tok->str());
+        const std::unordered_map<std::string, std::string>::const_iterator cOpIt = cAlternativeTokens.find(tok->str());
         if (cOpIt != cAlternativeTokens.end()) {
             alt.push_back(tok);
 
@@ -7474,7 +7474,7 @@ bool Tokenizer::simplifyCAlternativeTokens()
         return false;
 
     for (Token *tok: alt) {
-        const std::map<std::string, std::string>::const_iterator cOpIt = cAlternativeTokens.find(tok->str());
+        const std::unordered_map<std::string, std::string>::const_iterator cOpIt = cAlternativeTokens.find(tok->str());
         if (cOpIt != cAlternativeTokens.end())
             tok->str(cOpIt->second);
         else if (tok->str() == "not")