diff --git a/debug.h b/debug.h
index 6a867a1..a954839 100644
--- a/debug.h
+++ b/debug.h
@@ -10,7 +10,7 @@ private:
 	static int debug_level; // debug level set globally
 
 public:
-	Debug(int n);
+	explicit Debug(int n);
 	~Debug();
 
 	// Copy constructor and assignment operators are deleted to prevent extra destructor and constructor calls when chaining << operator
diff --git a/gpx.h b/gpx.h
index 800941b..142cb68 100644
--- a/gpx.h
+++ b/gpx.h
@@ -16,7 +16,7 @@ private:
 	gpx::GPX* root;
 
 public:
-	GPX(std::string path);
+	explicit GPX(std::string path);
 	~GPX();
 
 	Cache get_cache(std::string code);
diff --git a/heat.h b/heat.h
index f1d72a0..f8d9720 100644
--- a/heat.h
+++ b/heat.h
@@ -11,7 +11,7 @@ private:
 	const Map* mp;
 
 public:
-	Heat(const Map* m);
+	explicit Heat(const Map* m);
 
 	void generate(std::string filename, Caches& points, int stamp_size, std::string theme = "soft");
 	void generate_path(std::string filename, const Date_Caches& sorted);
diff --git a/ocdb.h b/ocdb.h
index 969ca68..610292e 100644
--- a/ocdb.h
+++ b/ocdb.h
@@ -26,7 +26,7 @@ private:
 	bool read_revision();
 
 public:
-	OCdb(std::string db_file);
+	explicit OCdb(std::string db_file);
 	~OCdb();
 
 	bool init(std::string json_file); // read db dump