Index: src/option_handler_rules.cc
===================================================================
--- src/option_handler_rules.cc	(revision 854)
+++ src/option_handler_rules.cc	(working copy)
@@ -320,7 +320,7 @@
   else if (arg == "mincost")
     value = torrent::ConnectionManager::iptos_mincost;
 
-  else if (!utils::Variable::string_to_value_unit_nothrow(arg.c_str(), &value, 16, 0))
+  else if (!utils::Variable::string_to_value_unit_nothrow(arg.c_str(), &value, 16, 1))
     throw torrent::input_error("Invalid TOS identifier.");
 
   cm->set_priority(value);
Index: src/utils/variable.cc
===================================================================
--- src/utils/variable.cc	(revision 854)
+++ src/utils/variable.cc	(working copy)
@@ -66,6 +66,9 @@
 
 const char*
 Variable::string_to_value_unit(const char* pos, value_type* value, int base, int unit) {
+  if (unit <= 0)
+    throw torrent::input_error("Variable::string_to_value_unit(...) received unit <= 0.");
+
   char* last;
   *value = strtoll(pos, &last, base);