diff --git a/build/build.tcl b/build/build.tcl
index f4433f40..ba0a640e 100644
--- a/build/build.tcl
+++ b/build/build.tcl
@@ -106,7 +106,11 @@ proc build_macsyma_portion {} {
 }
 
 set timeout 100
-expect_after timeout abort
+proc setup_timeout {} {
+    # Don't do this until after you've called "spawn", otherwise it'll cause a
+    # read from stdin which will return EOF if stdin isn't a tty.
+    expect_after timeout abort
+}
 
 set ip [ip_address [lindex $argv 0]]
 set gw [ip_address [lindex $argv 1]]
diff --git a/build/simh/build.tcl b/build/simh/build.tcl
index 43df068e..35119f7d 100644
--- a/build/simh/build.tcl
+++ b/build/simh/build.tcl
@@ -4,6 +4,8 @@ set emulator_escape "\034"
 
 proc start_salv {} {
     uplevel #0 {spawn pdp10 build/simh/init}
+    setup_timeout
+
     respond "sim>" "show ver\r"
     respond "sim>" "b tu1\r"
     expect "MTBOOT"
@@ -23,6 +25,7 @@ proc start_dskdmp {} {
 
 proc start_its {} {
     uplevel #0 {spawn pdp10 build/simh/boot}
+    setup_timeout
 }
 
 proc mount_tape {file} {