diff --git a/build/build.tcl b/build/build.tcl
index 1c2ed545..3f04fcfd 100644
--- a/build/build.tcl
+++ b/build/build.tcl
@@ -21,12 +21,22 @@ if {![info exists env(MACSYMA)]} {
     set env(MACSYMA) "yes"
 }
 
+proc cleanup {} {
+    global spawn_id
+    close -i $spawn_id
+    sleep 1
+    exec kill [exp_pid $spawn_id]
+}
+
 proc abort {} {
     puts ""
     puts "The last command timed out."
     exit 1
 }
 
+exit -onexit cleanup
+trap {exit 1} {SIGINT SIGTERM}
+
 proc type s {
     sleep .1
     foreach c [split $s ""] {