diff --git a/dbus/set.go b/dbus/set.go
index 17c5d485..c0b8fde1 100644
--- a/dbus/set.go
+++ b/dbus/set.go
@@ -14,28 +14,43 @@
 
 package dbus
 
+import (
+	"sync"
+)
+
 type set struct {
 	data map[string]bool
+	mu   sync.Mutex
 }
 
 func (s *set) Add(value string) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
 	s.data[value] = true
 }
 
 func (s *set) Remove(value string) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
 	delete(s.data, value)
 }
 
 func (s *set) Contains(value string) (exists bool) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
 	_, exists = s.data[value]
 	return
 }
 
 func (s *set) Length() int {
+	s.mu.Lock()
+	defer s.mu.Unlock()
 	return len(s.data)
 }
 
 func (s *set) Values() (values []string) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
 	for val := range s.data {
 		values = append(values, val)
 	}
@@ -43,5 +58,5 @@ func (s *set) Values() (values []string) {
 }
 
 func newSet() *set {
-	return &set{make(map[string]bool)}
+	return &set{data: make(map[string]bool)}
 }
diff --git a/dbus/subscription.go b/dbus/subscription.go
index f0f6aad9..7aff411d 100644
--- a/dbus/subscription.go
+++ b/dbus/subscription.go
@@ -15,6 +15,7 @@
 package dbus
 
 import (
+	"context"
 	"errors"
 	"log"
 	"time"
@@ -94,16 +95,26 @@ func (c *Conn) dispatch() {
 	}()
 }
 
-// SubscribeUnits returns two unbuffered channels which will receive all changed units every
-// interval.  Deleted units are sent as nil.
+// Deprecated: use SubscribeUnitsContext instead.
 func (c *Conn) SubscribeUnits(interval time.Duration) (<-chan map[string]*UnitStatus, <-chan error) {
-	return c.SubscribeUnitsCustom(interval, 0, func(u1, u2 *UnitStatus) bool { return *u1 != *u2 }, nil)
+	return c.SubscribeUnitsContext(context.Background(), interval)
+}
+
+// SubscribeUnitsContext returns two unbuffered channels which will receive all changed units every
+// interval.  Deleted units are sent as nil.
+func (c *Conn) SubscribeUnitsContext(ctx context.Context, interval time.Duration) (<-chan map[string]*UnitStatus, <-chan error) {
+	return c.SubscribeUnitsCustomContext(ctx, interval, 0, func(u1, u2 *UnitStatus) bool { return *u1 != *u2 }, nil)
 }
 
-// SubscribeUnitsCustom is like SubscribeUnits but lets you specify the buffer
+// Deprecated: use SubscribeUnitsCustomContext instead.
+func (c *Conn) SubscribeUnitsCustom(interval time.Duration, buffer int, isChanged func(*UnitStatus, *UnitStatus) bool, filterUnit func(string) bool) (<-chan map[string]*UnitStatus, <-chan error) {
+	return c.SubscribeUnitsCustomContext(context.Background(), interval, buffer, isChanged, filterUnit)
+}
+
+// SubscribeUnitsCustomContext is like SubscribeUnits but lets you specify the buffer
 // size of the channels, the comparison function for detecting changes and a filter
 // function for cutting down on the noise that your channel receives.
-func (c *Conn) SubscribeUnitsCustom(interval time.Duration, buffer int, isChanged func(*UnitStatus, *UnitStatus) bool, filterUnit func(string) bool) (<-chan map[string]*UnitStatus, <-chan error) {
+func (c *Conn) SubscribeUnitsCustomContext(ctx context.Context, interval time.Duration, buffer int, isChanged func(*UnitStatus, *UnitStatus) bool, filterUnit func(string) bool) (<-chan map[string]*UnitStatus, <-chan error) {
 	old := make(map[string]*UnitStatus)
 	statusChan := make(chan map[string]*UnitStatus, buffer)
 	errChan := make(chan error, buffer)
@@ -112,7 +123,7 @@ func (c *Conn) SubscribeUnitsCustom(interval time.Duration, buffer int, isChange
 		for {
 			timerChan := time.After(interval)
 
-			units, err := c.ListUnits()
+			units, err := c.ListUnitsContext(ctx)
 			if err == nil {
 				cur := make(map[string]*UnitStatus)
 				for i := range units {
@@ -145,7 +156,14 @@ func (c *Conn) SubscribeUnitsCustom(interval time.Duration, buffer int, isChange
 				errChan <- err
 			}
 
-			<-timerChan
+			select {
+			case <-timerChan:
+				continue
+			case <-ctx.Done():
+				close(statusChan)
+				close(errChan)
+				return
+			}
 		}
 	}()
 
diff --git a/dbus/subscription_set.go b/dbus/subscription_set.go
index dbe4aa88..173ca372 100644
--- a/dbus/subscription_set.go
+++ b/dbus/subscription_set.go
@@ -15,6 +15,7 @@
 package dbus
 
 import (
+	"context"
 	"time"
 )
 
@@ -29,16 +30,21 @@ func (s *SubscriptionSet) filter(unit string) bool {
 	return !s.Contains(unit)
 }
 
-// Subscribe starts listening for dbus events for all of the units in the set.
+// SubscribeContext starts listening for dbus events for all of the units in the set.
 // Returns channels identical to conn.SubscribeUnits.
-func (s *SubscriptionSet) Subscribe() (<-chan map[string]*UnitStatus, <-chan error) {
+func (s *SubscriptionSet) SubscribeContext(ctx context.Context) (<-chan map[string]*UnitStatus, <-chan error) {
 	// TODO: Make fully evented by using systemd 209 with properties changed values
-	return s.conn.SubscribeUnitsCustom(time.Second, 0,
+	return s.conn.SubscribeUnitsCustomContext(ctx, time.Second, 0,
 		mismatchUnitStatus,
 		func(unit string) bool { return s.filter(unit) },
 	)
 }
 
+// Deprecated: use SubscribeContext instead.
+func (s *SubscriptionSet) Subscribe() (<-chan map[string]*UnitStatus, <-chan error) {
+	return s.SubscribeContext(context.Background())
+}
+
 // NewSubscriptionSet returns a new subscription set.
 func (c *Conn) NewSubscriptionSet() *SubscriptionSet {
 	return &SubscriptionSet{newSet(), c}