diff --git a/CHANGES.md b/CHANGES.md
index 9c1f6a4..5b17325 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,8 +1,11 @@
 # bunyan Changelog
 
-## bunyan 0.12.1 (not yet released)
+## bunyan 0.13.0 (not yet released)
 
-(nothing yet)
+- [issue #31] Re-instate defines for the (uppercase) log level names (TRACE,
+  DEBUG, etc.) in `bunyan -c "..."` filtering condition code. E.g.:
+
+        $ ... | bunyan -c 'level >= ERROR'
 
 
 ## bunyan 0.12.0
diff --git a/bin/bunyan b/bin/bunyan
index 68c8ed5..467d615 100755
--- a/bin/bunyan
+++ b/bin/bunyan
@@ -329,6 +329,13 @@ function parseArgv(argv) {
   }
   args = newArgs;
 
+  var condDefines = [];
+  Object.keys(upperNameFromLevel).forEach(function (lvl) {
+    condDefines.push(
+      format("Object.prototype.%s = %s;", upperNameFromLevel[lvl], lvl));
+  });
+  condDefines = condDefines.join('\n') + '\n';
+
   var endOfOptions = false;
   while (args.length > 0) {
     var arg = args.shift();
@@ -388,7 +395,7 @@ function parseArgv(argv) {
         var condition = args.shift();
         parsed.conditions = parsed.conditions || [];
         var scriptName = 'bunyan-condition-'+parsed.conditions.length;
-        var script = vm.createScript(condition, scriptName);
+        var script = vm.createScript(condDefines + condition, scriptName);
         parsed.conditions.push(script);
         break;
       default: // arguments