diff --git a/src/OSspecific/Unix/regularExpression.H b/src/OSspecific/Unix/regularExpression.H
index dc574a4c9f..9924caef28 100644
--- a/src/OSspecific/Unix/regularExpression.H
+++ b/src/OSspecific/Unix/regularExpression.H
@@ -100,7 +100,7 @@ public:
     // Member functions
 
         //- Matches?
-        inline bool matches(const string& s)
+        inline bool matches(const string& s) const
         {
             size_t nmatch = 0;
             regmatch_t *pmatch = NULL;