diff --git a/run/src/main/scala/sbt/TrapExit.scala b/run/src/main/scala/sbt/TrapExit.scala
index 4b0de4f63..56980e3f6 100644
--- a/run/src/main/scala/sbt/TrapExit.scala
+++ b/run/src/main/scala/sbt/TrapExit.scala
@@ -242,10 +242,11 @@ private final class TrapExit(delegateManager: SecurityManager) extends SecurityM
 				val t = tref.get
 				if( (t eq null) || isDone(t))
 					unregister(id)
-				else
+				else {
 					f(t)
-				if(isDone(t))
-					unregister(id)
+					if(isDone(t))
+						unregister(id)
+				}
 			}
 		}
 	}