diff --git a/whisper/whisperv5/api.go b/whisper/whisperv5/api.go
index 5b5b649a49..d31cb64425 100644
--- a/whisper/whisperv5/api.go
+++ b/whisper/whisperv5/api.go
@@ -283,7 +283,7 @@ func (api *PublicWhisperAPI) Post(args PostArgs) error {
 
 	filter := api.whisper.GetFilter(args.FilterID)
 	if filter == nil && len(args.FilterID) > 0 {
-		info := fmt.Sprintf("Post: wrong filter id %d", args.FilterID)
+		info := fmt.Sprintf("Post: wrong filter id %s", args.FilterID)
 		glog.V(logger.Error).Infof(info)
 		return errors.New(info)
 	}
@@ -299,7 +299,7 @@ func (api *PublicWhisperAPI) Post(args PostArgs) error {
 		if (params.Topic == TopicType{}) {
 			sz := len(filter.Topics)
 			if sz < 1 {
-				info := fmt.Sprintf("Post: no topics in filter # %d", args.FilterID)
+				info := fmt.Sprintf("Post: no topics in filter # %s", args.FilterID)
 				glog.V(logger.Error).Infof(info)
 				return errors.New(info)
 			} else if sz == 1 {
diff --git a/whisper/whisperv5/api_test.go b/whisper/whisperv5/api_test.go
index 48536b84ba..ea0a2c40bc 100644
--- a/whisper/whisperv5/api_test.go
+++ b/whisper/whisperv5/api_test.go
@@ -250,7 +250,7 @@ func TestUnmarshalPostArgs(t *testing.T) {
 		t.Fatalf("wrong pow: %f.", a.PoW)
 	}
 	if a.FilterID != "test-filter-id" {
-		t.Fatalf("wrong FilterID: %d.", a.FilterID)
+		t.Fatalf("wrong FilterID: %s.", a.FilterID)
 	}
 	if !bytes.Equal(a.PeerID[:], a.Topic[:]) {
 		t.Fatalf("wrong PeerID: %x.", a.PeerID)
diff --git a/whisper/whisperv5/peer_test.go b/whisper/whisperv5/peer_test.go
index fc4f29ceef..223dd87620 100644
--- a/whisper/whisperv5/peer_test.go
+++ b/whisper/whisperv5/peer_test.go
@@ -187,7 +187,7 @@ func checkPropagation(t *testing.T) {
 		for i := 0; i < NumNodes; i++ {
 			f := nodes[i].shh.GetFilter(nodes[i].filerId)
 			if f == nil {
-				t.Fatalf("failed to get filterId %d from node %d.", nodes[i].filerId, i)
+				t.Fatalf("failed to get filterId %s from node %d.", nodes[i].filerId, i)
 			}
 
 			mail := f.Retrieve()