diff --git a/library/stringUtils.sol b/library/stringUtils.sol
index e6994c3..8203053 100644
--- a/library/stringUtils.sol
+++ b/library/stringUtils.sol
@@ -2,7 +2,7 @@ library StringUtils {
     /// @dev Does a byte-by-byte lexicographical comparison of two strings.
     /// @return a negative number if `_a` is smaller, zero if they are equal
     /// and a positive numbe if `_b` is smaller.
-    function compare(string _a, string _b) returns (int) {
+    function compare(string _a, string _b) public pure returns (int) {
         bytes memory a = bytes(_a);
         bytes memory b = bytes(_b);
         uint minLength = a.length;
@@ -21,11 +21,11 @@ library StringUtils {
             return 0;
     }
     /// @dev Compares two strings and returns true iff they are equal.
-    function equal(string _a, string _b) returns (bool) {
+    function equal(string _a, string _b) public pure returns (bool) {
         return compare(_a, _b) == 0;
     }
     /// @dev Finds the index of the first occurrence of _needle in _haystack
-    function indexOf(string _haystack, string _needle) returns (int)
+    function indexOf(string _haystack, string _needle) public pure returns (int)
     {
     	bytes memory h = bytes(_haystack);
     	bytes memory n = bytes(_needle);