diff --git a/userspace/engine/filter_evttype_resolver.cpp b/userspace/engine/filter_evttype_resolver.cpp
index 8b8a54c9..44d5a0c7 100644
--- a/userspace/engine/filter_evttype_resolver.cpp
+++ b/userspace/engine/filter_evttype_resolver.cpp
@@ -17,12 +17,11 @@ limitations under the License.
 #include "filter_evttype_resolver.h"
 #include <sinsp.h>
 
-using namespace std;
 using namespace libsinsp::filter;
 
 extern sinsp_evttables g_infotables;
 
-static bool is_evttype_operator(const string& op)
+static bool is_evttype_operator(const std::string& op)
 {
 	return op == "==" || op == "=" || op == "!=" || op == "in";
 }
@@ -44,7 +43,7 @@ void filter_evttype_resolver::visitor::inversion(falco_event_types& types)
 	}
 }
 
-void filter_evttype_resolver::visitor::evttypes(string evtname, falco_event_types& out)
+void filter_evttype_resolver::visitor::evttypes(const std::string& evtname, falco_event_types& out)
 {
 	// Fill in from 2 to PPM_EVENT_MAX-1. 0 and 1 are excluded as
 	// those are PPM_GENERIC_E/PPME_GENERIC_X
@@ -53,7 +52,7 @@ void filter_evttype_resolver::visitor::evttypes(string evtname, falco_event_type
 	{
 		// Skip unused events or events not matching the requested evtname
 		if(!(etable[i].flags & EF_UNUSED)
-			&& (evtname.empty() || string(etable[i].name) == evtname))
+			&& (evtname.empty() || std::string(etable[i].name) == evtname))
 		{
 			out.insert(i);
 		}
diff --git a/userspace/engine/filter_evttype_resolver.h b/userspace/engine/filter_evttype_resolver.h
index 3de0e35e..7858da97 100644
--- a/userspace/engine/filter_evttype_resolver.h
+++ b/userspace/engine/filter_evttype_resolver.h
@@ -157,7 +157,7 @@ public:
 		string is passed, all the available evttypes are collected
 		\param out The set to be filled with the evttypes
 	*/
-	inline void evttypes(std::string evtname, falco_event_types& out) const
+	inline void evttypes(const std::string& evtname, falco_event_types& out) const
 	{
 		falco_event_types evt_types;
 		visitor().evttypes(evtname, evt_types);
@@ -205,6 +205,6 @@ private:
 		void visit(libsinsp::filter::ast::unary_check_expr* e) override;
 		void visit(libsinsp::filter::ast::binary_check_expr* e) override;
 		void inversion(falco_event_types& types);
-		void evttypes(std::string evtname, falco_event_types& out);
+		void evttypes(const std::string& evtname, falco_event_types& out);
 	};
 };
diff --git a/userspace/falco/app_actions/print_support.cpp b/userspace/falco/app_actions/print_support.cpp
index d4ff0e9a..d0863c81 100644
--- a/userspace/falco/app_actions/print_support.cpp
+++ b/userspace/falco/app_actions/print_support.cpp
@@ -21,7 +21,7 @@ limitations under the License.
 
 using namespace falco::app;
 
-static std::string read_file(std::string &filename)
+static std::string read_file(const std::string &filename)
 {
 	std::ifstream t(filename);
 	std::string str((std::istreambuf_iterator<char>(t)),