diff --git a/render/selectors_test.go b/render/selectors_test.go
new file mode 100644
index 000000000..ee01e983b
--- /dev/null
+++ b/render/selectors_test.go
@@ -0,0 +1,62 @@
+package render_test
+
+import (
+	"testing"
+
+	"github.com/weaveworks/scope/render"
+	"github.com/weaveworks/scope/report"
+	"github.com/weaveworks/scope/test"
+	"github.com/weaveworks/scope/test/reflect"
+)
+
+func TestMakeRenderableNodes(t *testing.T) {
+
+	var (
+		newu64     = func(value uint64) *uint64 { return &value }
+		srcNodeID  = "srcNode"
+		dstNode1ID = "dstNode1"
+		dstNode2ID = "dstNode2"
+		srcNode    = report.MakeNode().
+				WithEdge(dstNode1ID, report.EdgeMetadata{EgressPacketCount: newu64(100), EgressByteCount: newu64(1000)}).
+				WithEdge(dstNode2ID, report.EdgeMetadata{EgressPacketCount: newu64(200), EgressByteCount: newu64(2000)})
+		dstNode1 = report.MakeNode()
+		dstNode2 = report.MakeNode()
+		topology = report.MakeTopology().
+				AddNode(srcNodeID, srcNode).
+				AddNode(dstNode1ID, dstNode1).
+				AddNode(dstNode2ID, dstNode2)
+	)
+
+	result := render.MakeRenderableNodes(topology)
+	mustLookup := func(id string) render.RenderableNode {
+		node, ok := result[id]
+		if !ok {
+			t.Fatalf("Expected result to contain node: %q, got: %v", id, result)
+		}
+		return node
+	}
+
+	// Source nodes should have the flattened edge metadata
+	{
+		have := mustLookup(srcNodeID).EdgeMetadata
+		want := report.EdgeMetadata{EgressPacketCount: newu64(300), EgressByteCount: newu64(3000)}
+		if !reflect.DeepEqual(want, have) {
+			t.Errorf(test.Diff(want, have))
+		}
+	}
+
+	// Result destination nodes should have the reverse of the source nodes
+	{
+		have := mustLookup(dstNode1ID).EdgeMetadata
+		want := report.EdgeMetadata{IngressPacketCount: newu64(100), IngressByteCount: newu64(1000)}
+		if !reflect.DeepEqual(want, have) {
+			t.Errorf(test.Diff(want, have))
+		}
+
+		have = mustLookup(dstNode2ID).EdgeMetadata
+		want = report.EdgeMetadata{IngressPacketCount: newu64(200), IngressByteCount: newu64(2000)}
+		if !reflect.DeepEqual(want, have) {
+			t.Errorf(test.Diff(want, have))
+		}
+	}
+}
diff --git a/report/edge_metadatas_internal_test.go b/report/edge_metadatas_internal_test.go
index b6277a50a..758398939 100644
--- a/report/edge_metadatas_internal_test.go
+++ b/report/edge_metadatas_internal_test.go
@@ -282,3 +282,34 @@ func TestEdgeMetadatasEncodingNil(t *testing.T) {
 }
 
 func newu64(value uint64) *uint64 { return &value }
+
+func TestEdgeMetadataDeepEquals(t *testing.T) {
+	for _, c := range []struct {
+		name string
+		a, b interface{}
+		want bool
+	}{
+		{
+			name: "zero values",
+			a:    EdgeMetadata{},
+			b:    EdgeMetadata{},
+			want: true,
+		},
+		{
+			name: "matching, but different pointers",
+			a:    EdgeMetadata{EgressPacketCount: newu64(3)},
+			b:    EdgeMetadata{EgressPacketCount: newu64(3)},
+			want: true,
+		},
+		{
+			name: "mismatching",
+			a:    EdgeMetadata{EgressPacketCount: newu64(3)},
+			b:    EdgeMetadata{EgressPacketCount: newu64(4)},
+			want: false,
+		},
+	} {
+		if have := reflect.DeepEqual(c.a, c.b); have != c.want {
+			t.Errorf("reflect.DeepEqual(%v, %v) != %v", c.a, c.b, c.want)
+		}
+	}
+}
diff --git a/report/sets.go b/report/sets.go
index 77067f9df..96d8cabec 100644
--- a/report/sets.go
+++ b/report/sets.go
@@ -27,11 +27,17 @@ func MakeSets() Sets {
 
 // Keys returns the keys for this set
 func (s Sets) Keys() []string {
+	if s.psMap == nil {
+		return nil
+	}
 	return s.psMap.Keys()
 }
 
 // Add the given value to the Sets.
 func (s Sets) Add(key string, value StringSet) Sets {
+	if s.psMap == nil {
+		s = EmptySets
+	}
 	if existingValue, ok := s.psMap.Lookup(key); ok {
 		value = value.Merge(existingValue.(StringSet))
 	}
@@ -42,6 +48,9 @@ func (s Sets) Add(key string, value StringSet) Sets {
 
 // Lookup returns the sets stored under key.
 func (s Sets) Lookup(key string) (StringSet, bool) {
+	if s.psMap == nil {
+		return EmptyStringSet, false
+	}
 	if value, ok := s.psMap.Lookup(key); ok {
 		return value.(StringSet), true
 	}
@@ -50,6 +59,9 @@ func (s Sets) Lookup(key string) (StringSet, bool) {
 
 // Size returns the number of elements
 func (s Sets) Size() int {
+	if s.psMap == nil {
+		return 0
+	}
 	return s.psMap.Size()
 }
 
@@ -88,6 +100,9 @@ func (s Sets) Copy() Sets {
 }
 
 func (s Sets) String() string {
+	if s.psMap == nil {
+		s = EmptySets
+	}
 	keys := []string{}
 	for _, k := range s.psMap.Keys() {
 		keys = append(keys, k)
@@ -105,9 +120,12 @@ func (s Sets) String() string {
 
 // DeepEqual tests equality with other Sets
 func (s Sets) DeepEqual(t Sets) bool {
-	if s.psMap.Size() != t.psMap.Size() {
+	if s.Size() != t.Size() {
 		return false
 	}
+	if s.Size() == 0 {
+		return true
+	}
 
 	equal := true
 	s.psMap.ForEach(func(k string, val interface{}) {
@@ -122,9 +140,11 @@ func (s Sets) DeepEqual(t Sets) bool {
 
 func (s Sets) toIntermediate() map[string]StringSet {
 	intermediate := map[string]StringSet{}
-	s.psMap.ForEach(func(key string, val interface{}) {
-		intermediate[key] = val.(StringSet)
-	})
+	if s.psMap != nil {
+		s.psMap.ForEach(func(key string, val interface{}) {
+			intermediate[key] = val.(StringSet)
+		})
+	}
 	return intermediate
 }