diff --git a/pkg/labels/labels.go b/pkg/labels/labels.go
index 38ec2ac0e94..86971d3f841 100644
--- a/pkg/labels/labels.go
+++ b/pkg/labels/labels.go
@@ -17,6 +17,7 @@ limitations under the License.
 package labels
 
 import (
+	"sort"
 	"strings"
 )
 
@@ -35,6 +36,8 @@ func (ls Set) String() string {
 	for key, value := range ls {
 		query = append(query, key+"="+value)
 	}
+	// Sort for determinism.
+	sort.StringSlice(query).Sort()
 	return strings.Join(query, ",")
 }
 
diff --git a/pkg/labels/labels_test.go b/pkg/labels/labels_test.go
index 76db00b951a..74db659acaa 100644
--- a/pkg/labels/labels_test.go
+++ b/pkg/labels/labels_test.go
@@ -29,7 +29,7 @@ func matches(t *testing.T, ls Set, want string) {
 func TestSetString(t *testing.T) {
 	matches(t, Set{"x": "y"}, "x=y")
 	matches(t, Set{"foo": "bar"}, "foo=bar")
-	matches(t, Set{"foo": "bar", "baz": "qup"}, "foo=bar,baz=qup")
+	matches(t, Set{"foo": "bar", "baz": "qup"}, "baz=qup,foo=bar")
 
 	// TODO: Make our label representation robust enough to handel labels
 	// with ",=!" characters in their names.