diff --git a/Makefile b/Makefile
index 797d6f6..338d79b 100644
--- a/Makefile
+++ b/Makefile
@@ -16,7 +16,7 @@ LABS=" lab1 lab2a lab2b lab2c lab2d lab3a lab3b lab4a lab4b "
 			"--exclude=src/main/mr-*" \
 			"--exclude=mrtmp.*" \
 			"--exclude=src/main/diff.out" \
-			"--exclude=src/main/mrmaster" \
+			"--exclude=src/main/mrcoordinator" \
 			"--exclude=src/main/mrsequential" \
 			"--exclude=src/main/mrworker" \
 			"--exclude=*.so" \
diff --git a/src/kvraft/test_test.go b/src/kvraft/test_test.go
index 162eb7e..df34365 100644
--- a/src/kvraft/test_test.go
+++ b/src/kvraft/test_test.go
@@ -37,11 +37,17 @@ func (log *OpLog) Read() []porcupine.Operation {
 	return ops
 }
 
+// to make sure timestamps use the monotonic clock, instead of computing
+// absolute timestamps with `time.Now().UnixNano()` (which uses the wall
+// clock), we measure time relative to `t0` using `time.Since(t0)`, which uses
+// the monotonic clock
+var t0 = time.Now()
+
 // get/put/putappend that keep counts
 func Get(cfg *config, ck *Clerk, key string, log *OpLog, cli int) string {
-	start := time.Now().UnixNano()
+	start := int64(time.Since(t0))
 	v := ck.Get(key)
-	end := time.Now().UnixNano()
+	end := int64(time.Since(t0))
 	cfg.op()
 	if log != nil {
 		log.Append(porcupine.Operation{
@@ -57,9 +63,9 @@ func Get(cfg *config, ck *Clerk, key string, log *OpLog, cli int) string {
 }
 
 func Put(cfg *config, ck *Clerk, key string, value string, log *OpLog, cli int) {
-	start := time.Now().UnixNano()
+	start := int64(time.Since(t0))
 	ck.Put(key, value)
-	end := time.Now().UnixNano()
+	end := int64(time.Since(t0))
 	cfg.op()
 	if log != nil {
 		log.Append(porcupine.Operation{
@@ -73,9 +79,9 @@ func Put(cfg *config, ck *Clerk, key string, value string, log *OpLog, cli int)
 }
 
 func Append(cfg *config, ck *Clerk, key string, value string, log *OpLog, cli int) {
-	start := time.Now().UnixNano()
+	start := int64(time.Since(t0))
 	ck.Append(key, value)
-	end := time.Now().UnixNano()
+	end := int64(time.Since(t0))
 	cfg.op()
 	if log != nil {
 		log.Append(porcupine.Operation{
diff --git a/src/main/test-mr.sh b/src/main/test-mr.sh
index 6e87891..1adc9d8 100644
--- a/src/main/test-mr.sh
+++ b/src/main/test-mr.sh
@@ -7,7 +7,7 @@
 # comment this out to run the tests without the Go race detector.
 RACE=-race
 
-if [ "$OSTYPE" = "darwin" ]
+if [[ "$OSTYPE" = "darwin"* ]]
 then
   if go version | grep 'go1.17.[012345]'
   then
@@ -30,7 +30,7 @@ else
   else
     # no timeout command
     TIMEOUT=
-    echo '*** Cannot find timeout command; proceeding anyway.'
+    echo '*** Cannot find timeout command; proceeding without timeouts.'
   fi
 fi
 if [ "$TIMEOUT" != "" ]
@@ -233,7 +233,7 @@ sleep 1
 # `jobs` ensures that any completed old processes from other tests
 # are not waited upon.
 jobs &> /dev/null
-if [ "$OSTYPE" = "darwin" ]
+if [[ "$OSTYPE" = "darwin"* ]]
 then
   # bash on the Mac doesn't have wait -n
   while [ ! -e $DF ]