diff --git a/source/Commands/CommandObjectExpression.cpp b/source/Commands/CommandObjectExpression.cpp
index ee14839..ed7824b 100644
--- a/source/Commands/CommandObjectExpression.cpp
+++ b/source/Commands/CommandObjectExpression.cpp
@@ -70,7 +70,7 @@
         break;
 
     case 'f':
-        error = Args::StringToFormat(option_arg, format);
+        error = Args::StringToFormat(option_arg, format, NULL);
         break;
         
     case 'o':