diff --git a/src/operators/contains.cc b/src/operators/contains.cc
index 7eaa3300..8bfb7349 100644
--- a/src/operators/contains.cc
+++ b/src/operators/contains.cc
@@ -21,14 +21,13 @@ namespace ModSecurity {
 namespace operators {
 
 bool Contains::evaluate(Assay *assay, const std::string &input) {
-    return input.find(this->param) != std::string::npos;
-}
+    bool contains = input.find(param) != std::string::npos;
 
-Contains::Contains(std::string _op, std::string _param,
-    bool negation)
-    : Operator() {
-    this->op = _op;
-    this->param = _param;
+    if (negation) {
+        return !contains;
+    }
+
+    return contains;
 }
 
 }  // namespace operators
diff --git a/src/operators/contains.h b/src/operators/contains.h
index c4abec21..af24e0e9 100644
--- a/src/operators/contains.h
+++ b/src/operators/contains.h
@@ -28,7 +28,8 @@ namespace operators {
 class Contains : public Operator {
  public:
     /** @ingroup ModSecurity_Operator */
-    Contains(std::string o, std::string p, bool i);
+    Contains(std::string op, std::string param, bool negation)
+        : Operator(op, param, negation) { }
     bool evaluate(Assay *assay, const std::string &exp) override;
 };