diff --git a/t/bellow.do b/t/bellow.do
index 748ef62..fa98f55 100644
--- a/t/bellow.do
+++ b/t/bellow.do
@@ -1,2 +1,3 @@
 redo-ifchange LD yellow.o
 ./LD bellow yellow.o
+./sleep 2
diff --git a/t/hello.do b/t/hello.do
index e2c2bb9..93794ee 100644
--- a/t/hello.do
+++ b/t/hello.do
@@ -1,2 +1,3 @@
 redo-ifchange LD hello.o
+./sleep 1
 ./LD hello hello.o
diff --git a/t/hello.o.do b/t/hello.o.do
index 543bf85..ae44f5b 100644
--- a/t/hello.o.do
+++ b/t/hello.o.do
@@ -1,3 +1,4 @@
 redo-ifchange CC hello.c /usr/include/stdio.h
 redo-ifcreate stdio.h
+./sleep 3
 ./CC hello.c
diff --git a/t/sleep b/t/sleep
new file mode 100755
index 0000000..7322c5a
--- /dev/null
+++ b/t/sleep
@@ -0,0 +1,4 @@
+PATH=/bin:/usr/bin
+if [ -n "$SLEEP" ]; then
+	exec sleep "$@"
+fi
diff --git a/t/yellow.do b/t/yellow.do
index 69d6689..dbcf36b 100644
--- a/t/yellow.do
+++ b/t/yellow.do
@@ -1,2 +1,3 @@
 redo-ifchange LD yellow.o
+./sleep 1.5
 ./LD yellow yellow.o
diff --git a/t/yellow.o.do b/t/yellow.o.do
index 14bc756..a8101e5 100644
--- a/t/yellow.o.do
+++ b/t/yellow.o.do
@@ -1,2 +1,3 @@
 redo-ifchange CC hello.c
+./sleep 2
 gcc -o $3 -c hello.c