diff --git a/headers/modsecurity/rule.h b/headers/modsecurity/rule.h
index a76b5c69..393b4144 100644
--- a/headers/modsecurity/rule.h
+++ b/headers/modsecurity/rule.h
@@ -91,9 +91,9 @@ class Rule {
         std::string value, std::shared_ptr<RuleMessage> rm);
     void executeActionsIndependentOfChainedRuleResult(Transaction *trasn,
         bool *b, std::shared_ptr<RuleMessage> ruleMessage);
-    void updateMatchedVars(Transaction *trasn, std::string key,
-        std::string value);
-    void cleanMatchedVars(Transaction *trasn);
+    inline void updateMatchedVars(Transaction *trasn, const std::string &key,
+        const std::string &value);
+    inline void cleanMatchedVars(Transaction *trasn);
 
     std::vector<actions::Action *> getActionsByName(const std::string& name,
         Transaction *t);
diff --git a/src/rule.cc b/src/rule.cc
index 3f38f05f..42b42862 100644
--- a/src/rule.cc
+++ b/src/rule.cc
@@ -241,8 +241,8 @@ void Rule::cleanUpActions() {
 }
 
 
-void Rule::updateMatchedVars(Transaction *trans, std::string key,
-    std::string value) {
+inline void Rule::updateMatchedVars(Transaction *trans, const std::string &key,
+    const std::string &value) {
 #ifndef NO_LOGS
     trans->debug(9, "Matched vars updated.");
 #endif
@@ -254,7 +254,7 @@ void Rule::updateMatchedVars(Transaction *trans, std::string key,
 }
 
 
-void Rule::cleanMatchedVars(Transaction *trans) {
+inline void Rule::cleanMatchedVars(Transaction *trans) {
 #ifndef NO_LOGS
     trans->debug(9, "Matched vars cleaned.");
 #endif