diff --git a/config.go b/config.go
index ac34589640..cb7e985ca2 100644
--- a/config.go
+++ b/config.go
@@ -43,7 +43,7 @@ func DaemonConfigFromJob(job *engine.Job) *DaemonConfig {
 	} else {
 		config.BridgeIface = DefaultNetworkBridge
 	}
-	if mtu := job.GetenvInt("Mtu"); mtu != -1 {
+	if mtu := job.GetenvInt("Mtu"); mtu != 0 {
 		config.Mtu = mtu
 	} else {
 		config.Mtu = DefaultNetworkMtu
diff --git a/engine/env.go b/engine/env.go
index e000fe26b1..d6ca4ec07b 100644
--- a/engine/env.go
+++ b/engine/env.go
@@ -60,7 +60,7 @@ func (env *Env) GetInt64(key string) int64 {
 	s := strings.Trim(env.Get(key), " \t")
 	val, err := strconv.ParseInt(s, 10, 64)
 	if err != nil {
-		return -1
+		return 0
 	}
 	return val
 }
diff --git a/engine/env_test.go b/engine/env_test.go
index 419c47491e..c7079ff942 100644
--- a/engine/env_test.go
+++ b/engine/env_test.go
@@ -62,7 +62,7 @@ func TestSetenvInt(t *testing.T) {
 	if val := job.GetenvInt("bar"); val != 42 {
 		t.Fatalf("GetenvInt returns incorrect value: %d", val)
 	}
-	if val := job.GetenvInt("nonexistent"); val != -1 {
+	if val := job.GetenvInt("nonexistent"); val != 0 {
 		t.Fatalf("GetenvInt returns incorrect value: %d", val)
 	}
 }
diff --git a/engine/job.go b/engine/job.go
index 181eaa80c7..c2eadccc1b 100644
--- a/engine/job.go
+++ b/engine/job.go
@@ -102,6 +102,10 @@ func (job *Job) String() string {
 	return fmt.Sprintf("%s.%s%s", job.Eng, job.CallString(), job.StatusString())
 }
 
+func (job *Job) EnvExists(key string) (value bool) {
+	return job.env.Exists(key)
+}
+
 func (job *Job) Getenv(key string) (value string) {
 	return job.env.Get(key)
 }
diff --git a/server.go b/server.go
index 27c27f25de..90a8bb3ed8 100644
--- a/server.go
+++ b/server.go
@@ -1083,7 +1083,7 @@ func (srv *Server) Containers(job *engine.Job) engine.Status {
 	}, -1)
 
 	for _, container := range srv.runtime.List() {
-		if !container.State.IsRunning() && !all && n == -1 && since == "" && before == "" {
+		if !container.State.IsRunning() && !all && n <= 0 && since == "" && before == "" {
 			continue
 		}
 		if before != "" && !foundBefore {
@@ -1092,7 +1092,7 @@ func (srv *Server) Containers(job *engine.Job) engine.Status {
 			}
 			continue
 		}
-		if displayed == n {
+		if n > 0 && displayed == n {
 			break
 		}
 		if container.ID == since || utils.TruncateID(container.ID) == since {
@@ -1742,7 +1742,7 @@ func (srv *Server) ContainerCreate(job *engine.Job) engine.Status {
 		return engine.StatusErr
 	}
 	config := ContainerConfigFromJob(job)
-	if config.Memory > 0 && config.Memory < 524288 {
+	if config.Memory != 0 && config.Memory < 524288 {
 		job.Errorf("Minimum memory limit allowed is 512k")
 		return engine.StatusErr
 	}
@@ -1798,10 +1798,12 @@ func (srv *Server) ContainerRestart(job *engine.Job) engine.Status {
 		job.Errorf("Usage: %s CONTAINER\n", job.Name)
 		return engine.StatusErr
 	}
-	name := job.Args[0]
-	t := job.GetenvInt("t")
-	if t == -1 {
-		t = 10
+	var (
+		name = job.Args[0]
+		t    = 10
+	)
+	if job.EnvExists("t") {
+		t = job.GetenvInt("t")
 	}
 	if container := srv.runtime.Get(name); container != nil {
 		if err := container.Restart(int(t)); err != nil {
@@ -2239,10 +2241,12 @@ func (srv *Server) ContainerStop(job *engine.Job) engine.Status {
 		job.Errorf("Usage: %s CONTAINER\n", job.Name)
 		return engine.StatusErr
 	}
-	name := job.Args[0]
-	t := job.GetenvInt("t")
-	if t == -1 {
-		t = 10
+	var (
+		name = job.Args[0]
+		t    = 10
+	)
+	if job.EnvExists("t") {
+		t = job.GetenvInt("t")
 	}
 	if container := srv.runtime.Get(name); container != nil {
 		if err := container.Stop(int(t)); err != nil {