diff --git a/common/modules/io.jsm b/common/modules/io.jsm
index 9b5f1492..de126f50 100644
--- a/common/modules/io.jsm
+++ b/common/modules/io.jsm
@@ -424,6 +424,8 @@ var IO = Module("io", {
 
         if (!file || !file.exists()) {
             util.dactyl.echoerr("Command not found: " + program);
+            if (callable(blocking))
+                util.trapErrors(blocking);
             return -1;
         }