diff --git a/t/010-jobserver/.gitignore b/t/010-jobserver/.gitignore
new file mode 100644
index 0000000..7430e1d
--- /dev/null
+++ b/t/010-jobserver/.gitignore
@@ -0,0 +1,6 @@
+*.end
+*.start
+*.sub
+*.spin
+*.log
+*.x
diff --git a/t/010-jobserver/all.do b/t/010-jobserver/all.do
new file mode 100644
index 0000000..85cc9b1
--- /dev/null
+++ b/t/010-jobserver/all.do
@@ -0,0 +1,13 @@
+# We put the -j options at this toplevel to detect an earlier bug
+# where the sub-jobserver wasn't inherited by sub-sub-processes, which
+# accidentally reverted to the parent jobserver instead.
+
+redo -j1 serialtest
+
+# Capture log output to parallel.log to hide the (intentional since we're
+# testing it) scary warning from redo about overriding the jobserver.
+echo 'parallel test...' >&2
+if ! redo -j10 paralleltest 2>parallel.log; then
+	cat parallel.log >&2
+	exit 99
+fi
diff --git a/t/010-jobserver/clean.do b/t/010-jobserver/clean.do
new file mode 100644
index 0000000..80aa8ab
--- /dev/null
+++ b/t/010-jobserver/clean.do
@@ -0,0 +1,2 @@
+rm -f *~ .*~ *.log *.sub *.spin *.x *.start *.end \
+	first second parallel parallel2
diff --git a/t/010-jobserver/default.spin.do b/t/010-jobserver/default.spin.do
new file mode 100644
index 0000000..293f924
--- /dev/null
+++ b/t/010-jobserver/default.spin.do
@@ -0,0 +1,4 @@
+for d in 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19; do
+	redo $2.$d.x
+done
+echo hello
diff --git a/t/010-jobserver/default.x.do b/t/010-jobserver/default.x.do
new file mode 100644
index 0000000..4662694
--- /dev/null
+++ b/t/010-jobserver/default.x.do
@@ -0,0 +1 @@
+echo world
diff --git a/t/010-jobserver/first.do b/t/010-jobserver/first.do
new file mode 100644
index 0000000..2835c19
--- /dev/null
+++ b/t/010-jobserver/first.do
@@ -0,0 +1,24 @@
+# in case we're (erroneously) running in parallel, give second.do some
+# time to start but not finish.
+echo 'first sleep' >&2
+sleep 1
+
+# Because of --shuffle, we can't be sure if first or second ran first, but
+# because all.do uses -j1, we *should* expect that if second ran first, it
+# at least ran to completion before we ran at all.
+if [ -e second.start ]; then
+	echo 'first: second already started before we did...' >&2
+	[ -e second.end ] || exit 21
+	echo 'first: ...and it finished as it should.' >&2
+	# no sense continuing the test; can't test anything if second already
+	# ran.
+	exit 0
+fi
+echo 'first: second has not started yet, good.' >&2
+
+echo 'first spin' >&2
+redo 1.a.spin
+[ -e 1.a.spin ] || exit 11
+echo 'first spin complete' >&2
+
+! [ -e second.start ] || exit 22
diff --git a/t/010-jobserver/parallel.do b/t/010-jobserver/parallel.do
new file mode 100644
index 0000000..7be7592
--- /dev/null
+++ b/t/010-jobserver/parallel.do
@@ -0,0 +1,6 @@
+# We should be running in parallel with a jobserver shared with second.do.
+# Give second.do some time to start but not finish.
+sleep 1
+
+[ -e parallel2.start ] || exit 31
+! [ -e parallel2.end ] || exit 32
diff --git a/t/010-jobserver/parallel2.do b/t/010-jobserver/parallel2.do
new file mode 100644
index 0000000..ac83526
--- /dev/null
+++ b/t/010-jobserver/parallel2.do
@@ -0,0 +1,4 @@
+rm -f $1.start $1.end
+: >$1.start
+sleep 2
+: >$1.end
diff --git a/t/010-jobserver/paralleltest.do b/t/010-jobserver/paralleltest.do
new file mode 100644
index 0000000..0fb3203
--- /dev/null
+++ b/t/010-jobserver/paralleltest.do
@@ -0,0 +1,7 @@
+# Test that -j2 really gives us parallel builds with their own tokens.
+# (It's hard to test for sure that we have our own tokens, but if we're
+# sharing with other tests, we can't be sure that parallel2 will run while
+# parallel is running, and the race condition will make this test at least
+# be flakey instead of pass, which means there's a bug.)
+rm -f *.sub *.spin *.x *.log parallel *.start *.end
+redo parallel parallel2
diff --git a/t/010-jobserver/second.do b/t/010-jobserver/second.do
new file mode 100644
index 0000000..de732b4
--- /dev/null
+++ b/t/010-jobserver/second.do
@@ -0,0 +1,8 @@
+rm -f $1.start $1.end
+echo 'second start' >&2
+: >$1.start
+redo 2.x
+echo 'second sleep' >&2
+redo-ifchange first  # wait until 'first' finishes, if it's running
+echo 'second end' >&2
+: >$1.end
diff --git a/t/010-jobserver/serialtest.do b/t/010-jobserver/serialtest.do
new file mode 100644
index 0000000..4c2bb7e
--- /dev/null
+++ b/t/010-jobserver/serialtest.do
@@ -0,0 +1,4 @@
+# Test that -j1 really serializes all sub-redo processes.
+rm -f *.sub *.spin *.x first second *.start *.end
+redo first second
+
diff --git a/t/203-make/.gitignore b/t/203-make/.gitignore
index 038beb4..76809a5 100644
--- a/t/203-make/.gitignore
+++ b/t/203-make/.gitignore
@@ -1,2 +1,3 @@
+*.log
 *.out
 whichmake
diff --git a/t/203-make/all.do b/t/203-make/all.do
index 3b2c06f..3a665ea 100644
--- a/t/203-make/all.do
+++ b/t/203-make/all.do
@@ -12,7 +12,12 @@ run() {
     redo y
 
     rm -f *.out
-    redo -j10 y
+    # Capture output to y.log because we know this intentionally generates
+    # a scary-looking redo warning (overriding the jobserver).
+    if ! redo -j10 y 2>y.log; then
+        cat y.log
+        exit 99
+    fi
 }
 
 run
diff --git a/t/203-make/clean.do b/t/203-make/clean.do
index bac26b4..4eb03b8 100644
--- a/t/203-make/clean.do
+++ b/t/203-make/clean.do
@@ -1 +1 @@
-rm -f *~ .*~ *.out whichmake
+rm -f *~ .*~ *.out whichmake *.log