diff --git a/server/util.go b/server/util.go
index 44b0d95ab2..c77222bfe6 100644
--- a/server/util.go
+++ b/server/util.go
@@ -135,17 +135,18 @@ func AppendJSON(cdc *wire.Codec, baseJSON []byte, key string, value json.RawMess
 	return json.RawMessage(bz), err
 }
 
-// SortedJSON takes any JSON and returns it sorted by keys.
-// This can be used to sort JSON which will be returned by GetSignBytes,
+// SortedJSON takes any JSON and returns it sorted by keys. Also, all white-spaces
+// are removed.
+// This method can be used to canonicalize JSON to be returned by GetSignBytes,
 // e.g. for the ledger integration.
-// If the passed JSON isn't valid this will fail.
+// If the passed JSON isn't valid it will return an error.
 func SortJSON(toSortJSON []byte) ([]byte, error) {
 	var c interface{}
 	err := json.Unmarshal(toSortJSON, &c)
 	if err != nil {
 		return nil, err
 	}
-	js, err := json.MarshalIndent(c, "", " ")
+	js, err := json.Marshal(c)
 	if err != nil {
 		return nil, err
 	}
diff --git a/server/util_test.go b/server/util_test.go
index a207558f39..301215e1a4 100644
--- a/server/util_test.go
+++ b/server/util_test.go
@@ -40,5 +40,32 @@ func TestAppendJSON(t *testing.T) {
 }
 
 func TestSortJSON(t *testing.T) {
-	// TODO add testcases of several types
+	cases := []struct {
+		unsortedJson string
+		want         string
+		wantErr      bool
+	}{
+		// simple case
+		{unsortedJson: `{"cosmos":"foo", "atom":"bar",  "tendermint":"foobar"}`,
+			want: `{"atom":"bar","cosmos":"foo","tendermint":"foobar"}`, wantErr: false},
+		// failing case (invalid JSON):
+		{unsortedJson: `"cosmos":"foo",,,, "atom":"bar",  "tendermint":"foobar"}`,
+			want: "", wantErr: true},
+		// genesis.json
+		{unsortedJson: `{"consensus_params":{"block_size_params":{"max_bytes":22020096,"max_txs":100000,"max_gas":-1},"tx_size_params":{"max_bytes":10240,"max_gas":-1},"block_gossip_params":{"block_part_size_bytes":65536},"evidence_params":{"max_age":100000}},"validators":[{"pub_key":{"type":"AC26791624DE60","value":"c7UMMAbjFuc5GhGPy0E5q5tefy12p9Tq0imXqdrKXwo="},"power":100,"name":""}],"app_hash":"","genesis_time":"2018-05-11T15:52:25.424795506Z","chain_id":"test-chain-Q6VeoW","app_state":{"accounts":[{"address":"718C9C23F98C9642569742ADDD9F9AB9743FBD5D","coins":[{"denom":"Token","amount":1000},{"denom":"steak","amount":50}]}],"stake":{"pool":{"total_supply":50,"bonded_shares":"0","unbonded_shares":"0","bonded_pool":0,"unbonded_pool":0,"inflation_last_time":0,"inflation":"7/100"},"params":{"inflation_rate_change":"13/100","inflation_max":"1/5","inflation_min":"7/100","goal_bonded":"67/100","max_validators":100,"bond_denom":"steak"},"candidates":null,"bonds":null}}}`,
+			want: `{"app_hash":"","app_state":{"accounts":[{"address":"718C9C23F98C9642569742ADDD9F9AB9743FBD5D","coins":[{"amount":1000,"denom":"Token"},{"amount":50,"denom":"steak"}]}],"stake":{"bonds":null,"candidates":null,"params":{"bond_denom":"steak","goal_bonded":"67/100","inflation_max":"1/5","inflation_min":"7/100","inflation_rate_change":"13/100","max_validators":100},"pool":{"bonded_pool":0,"bonded_shares":"0","inflation":"7/100","inflation_last_time":0,"total_supply":50,"unbonded_pool":0,"unbonded_shares":"0"}}},"chain_id":"test-chain-Q6VeoW","consensus_params":{"block_gossip_params":{"block_part_size_bytes":65536},"block_size_params":{"max_bytes":22020096,"max_gas":-1,"max_txs":100000},"evidence_params":{"max_age":100000},"tx_size_params":{"max_bytes":10240,"max_gas":-1}},"genesis_time":"2018-05-11T15:52:25.424795506Z","validators":[{"name":"","power":100,"pub_key":{"type":"AC26791624DE60","value":"c7UMMAbjFuc5GhGPy0E5q5tefy12p9Tq0imXqdrKXwo="}}]}`,
+			wantErr: false},
+		// from the TXSpec:
+		{unsortedJson: `{"chain_id":"test-chain-1","sequence":1,"fee_bytes":{"amount":[{"amount":5,"denom":"photon"}],"gas":10000},"msg_bytes":{"inputs":[{"address":"696E707574","coins":[{"amount":10,"denom":"atom"}]}],"outputs":[{"address":"6F7574707574","coins":[{"amount":10,"denom":"atom"}]}]},"alt_bytes":null}`,
+			want:    `{"alt_bytes":null,"chain_id":"test-chain-1","fee_bytes":{"amount":[{"amount":5,"denom":"photon"}],"gas":10000},"msg_bytes":{"inputs":[{"address":"696E707574","coins":[{"amount":10,"denom":"atom"}]}],"outputs":[{"address":"6F7574707574","coins":[{"amount":10,"denom":"atom"}]}]},"sequence":1}`,
+			wantErr: false},
+	}
+
+	for _, tc := range cases {
+		got, err := SortJSON([]byte(tc.unsortedJson))
+		if tc.wantErr != (err != nil) {
+			t.Fatalf("got %t, want: %t, err=%s", err != nil, tc.wantErr, err)
+		}
+		require.Equal(t, string(got), tc.want)
+	}
 }