diff --git a/lib/command.rb b/lib/command.rb
index 1f5bb366b3e6cddd412028c0e862eb6911e56956..0645c659a7044bfcc3b4fbcdac6995678fc473ed 100644
--- a/lib/command.rb
+++ b/lib/command.rb
@@ -104,6 +104,7 @@ class Command
 			}.catch_only(Timeout) { nil }.catch_only(FinalStanza) { |e|
 				@blather << e.stanza
 			}.catch do |e|
+				e = RuntimeError.new(e) if e.is_a?(String)
 				send_final_error(e)
 				EMPromise.reject(e)
 			end