diff --git a/pkg/mapper/fakes.go b/pkg/mapper/fakes.go
index b973499802..bca3970711 100644
--- a/pkg/mapper/fakes.go
+++ b/pkg/mapper/fakes.go
@@ -35,3 +35,7 @@ func NewFakeClusterServiceMapper(returnError bool) ClusterServiceMapper {
 func (f *fakeClusterServiceMapper) Services(ing *v1beta1.Ingress) (map[v1beta1.IngressBackend]v1.Service, error) {
 	return nil, fmt.Errorf("fake error")
 }
+
+func (f *fakeClusterServiceMapper) SetExpectedServices(expectedSvcs []string) {
+	return
+}
diff --git a/pkg/mapper/interfaces.go b/pkg/mapper/interfaces.go
index d05f3bf0e8..73207c4251 100644
--- a/pkg/mapper/interfaces.go
+++ b/pkg/mapper/interfaces.go
@@ -23,4 +23,5 @@ import (
 // Services it defines for a specific cluster,
 type ClusterServiceMapper interface {
 	Services(ing *v1beta1.Ingress) (map[v1beta1.IngressBackend]v1.Service, error)
+	SetExpectedServices(expectedSvcs []string)
 }
diff --git a/pkg/mapper/mapper.go b/pkg/mapper/mapper.go
index 85fd591aa8..2ebe338906 100644
--- a/pkg/mapper/mapper.go
+++ b/pkg/mapper/mapper.go
@@ -20,6 +20,7 @@ import (
 	multierror "github.com/hashicorp/go-multierror"
 	"k8s.io/api/core/v1"
 	"k8s.io/api/extensions/v1beta1"
+	"k8s.io/ingress-gce/pkg/utils"
 )
 
 // Implements ClusterServiceMapper
@@ -38,14 +39,10 @@ var _ ClusterServiceMapper = &clusterServiceMapper{}
 func NewClusterServiceMapper(
 	svcGetter func(svcName string, namespace string) (*v1.Service, error),
 	expectedSvcs []string) ClusterServiceMapper {
-	es := make(map[string]bool)
-	if expectedSvcs == nil {
-		return &clusterServiceMapper{svcGetter, es}
+	return &clusterServiceMapper{
+		svcGetter,
+		utils.StringsToKeyMap(expectedSvcs),
 	}
-	for _, expectedSvc := range expectedSvcs {
-		es[expectedSvc] = true
-	}
-	return &clusterServiceMapper{svcGetter, es}
 }
 
 // Services returns a mapping for a cluster of IngressBackend -> Service given an Ingress.
@@ -91,6 +88,13 @@ Loop:
 	return backendToService, result.ErrorOrNil()
 }
 
+// SetExpectedServices makes the mapper aware of services that are expected
+// to exist in the cluster. Multiple calls to this function will overwrite
+// any previous state.
+func (c *clusterServiceMapper) SetExpectedServices(expectedSvcs []string) {
+	c.expectedSvcs = utils.StringsToKeyMap(expectedSvcs)
+}
+
 // expectedToExist returns true if the provided service name is expected to exist.
 func (c *clusterServiceMapper) expectedToExist(svcName string) bool {
 	if _, ok := c.expectedSvcs[svcName]; !ok && len(c.expectedSvcs) > 0 {
diff --git a/pkg/utils/utils.go b/pkg/utils/utils.go
index be7f1c005e..4a6b2d71a0 100644
--- a/pkg/utils/utils.go
+++ b/pkg/utils/utils.go
@@ -180,3 +180,11 @@ func BackendServiceComparablePath(url string) string {
 	}
 	return fmt.Sprintf("global/%s", path_parts[1])
 }
+
+func StringsToKeyMap(strings []string) map[string]bool {
+	m := make(map[string]bool)
+	for _, s := range strings {
+		m[s] = true
+	}
+	return m
+}