diff --git a/ml_string.cpp b/ml_string.cpp
index f527078..5473a2c 100644
--- a/ml_string.cpp
+++ b/ml_string.cpp
@@ -118,7 +118,7 @@ std::string string_trim(std::string s, const std::string &chars_to_trim, const s
 	return s;
 }
 
-std::string string_padd(const std::string &str, int pad_len, char fill_char, bool from_right) {
+std::string string_padd(const std::string &str, size_t pad_len, char fill_char, bool from_right) {
 	auto str_len = str.length();
 
 	if (str_len == pad_len)
@@ -148,7 +148,7 @@ std::string string_substring(const std::string & str, long pos, long count) {
 	return str.substr(start_pos, count);
 }
 
-size_t string_find_substr(const std::string & str, const std::string & pattern, long pos) {
+size_t string_find_substr(const std::string & str, const std::string & pattern, size_t pos) {
 	if (pos >= str.size()) {
 		throw std::invalid_argument("Invalid parameter(s) for string-find.");
 	}
diff --git a/ml_string.h b/ml_string.h
index 3e25998..0a25e42 100644
--- a/ml_string.h
+++ b/ml_string.h
@@ -18,8 +18,8 @@ std::string string_lucase(std::string s, const std::string &strcase);
 
 std::string string_trim(std::string s, const std::string &chars_to_trim, const std::string &rltrim);
 
-std::string string_padd(const std::string & str, int pad_len, char fill_char, bool from_right);
+std::string string_padd(const std::string & str, size_t pad_len, char fill_char, bool from_right);
 
 std::string string_substring(const std::string & str, long pos, long count);
 
-size_t string_find_substr(const std::string & str, const std::string & pattern, long pos);
+size_t string_find_substr(const std::string & str, const std::string & pattern, size_t pos);