diff --git a/web/api/legacy/api_test.go b/web/api/legacy/api_test.go
index 2ecb7f9df..34bf764ef 100644
--- a/web/api/legacy/api_test.go
+++ b/web/api/legacy/api_test.go
@@ -55,20 +55,25 @@ func TestQuery(t *testing.T) {
 			status:   http.StatusOK,
 			bodyRe:   `{"type":"error","value":"Parse error at char 1: no expression found in input","version":1}`,
 		},
+		{
+			queryStr: "expr=1.4",
+			status:   http.StatusOK,
+			bodyRe:   `{"type":"scalar","value":"1.4","version":1}`,
+		},
 		{
 			queryStr: "expr=testmetric",
 			status:   http.StatusOK,
-			bodyRe:   `{"type":"vector","value":\[\{"metric":{"__name__":"testmetric"},"value":"0","timestamp":\d+\.\d+}\],"version":1\}`,
+			bodyRe:   `{"type":"vector","value":\[{"metric":{"__name__":"testmetric"},"value":"0","timestamp":\d+\.\d+}\],"version":1}`,
 		},
 		{
 			queryStr: "expr=testmetric&timestamp=" + testTimestamp.String(),
 			status:   http.StatusOK,
-			bodyRe:   `{"type":"vector","value":\[\{"metric":{"__name__":"testmetric"},"value":"0","timestamp":` + testTimestamp.String() + `}\],"version":1\}`,
+			bodyRe:   `{"type":"vector","value":\[{"metric":{"__name__":"testmetric"},"value":"0","timestamp":` + testTimestamp.String() + `}\],"version":1}`,
 		},
 		{
 			queryStr: "expr=testmetric&timestamp=" + testTimestamp.Add(-time.Hour).String(),
 			status:   http.StatusOK,
-			bodyRe:   `{"type":"vector","value":\[\],"version":1\}`,
+			bodyRe:   `{"type":"vector","value":\[\],"version":1}`,
 		},
 		{
 			queryStr: "timestamp=invalid",
diff --git a/web/api/legacy/query.go b/web/api/legacy/query.go
index 511d75bc8..d0e2a9fac 100644
--- a/web/api/legacy/query.go
+++ b/web/api/legacy/query.go
@@ -133,11 +133,16 @@ func (pv plainVec) String() string {
 // which does not fit the response format for the legacy API.
 type plainScalar promql.Scalar
 
-func (pv plainScalar) Type() promql.ExprType {
+func (ps plainScalar) MarshalJSON() ([]byte, error) {
+	s := strconv.FormatFloat(float64(ps.Value), 'f', -1, 64)
+	return json.Marshal(&s)
+}
+
+func (plainScalar) Type() promql.ExprType {
 	return promql.ExprScalar
 }
 
-func (pv plainScalar) String() string {
+func (plainScalar) String() string {
 	return ""
 }