diff --git a/api/server/server_unit_test.go b/api/server/server_unit_test.go
index 3fc1cea064..3dbba640ff 100644
--- a/api/server/server_unit_test.go
+++ b/api/server/server_unit_test.go
@@ -70,7 +70,7 @@ func TestGetVersion(t *testing.T) {
 	eng.Register("version", func(job *engine.Job) engine.Status {
 		called = true
 		v := &engine.Env{}
-		v.Set("Version", "42.1")
+		v.SetJson("Version", "42.1")
 		v.Set("ApiVersion", "1.1.1.1.1")
 		v.Set("GoVersion", "2.42")
 		v.Set("Os", "Linux")
diff --git a/engine/env.go b/engine/env.go
index 1da3ae52e0..c43a5ec971 100644
--- a/engine/env.go
+++ b/engine/env.go
@@ -194,7 +194,25 @@ func (env *Env) SetAuto(k string, v interface{}) {
 }
 
 func (env *Env) Encode(dst io.Writer) error {
-	return json.NewEncoder(dst).Encode(env.Map())
+	m := make(map[string]interface{})
+	for k, v := range env.Map() {
+		var val interface{}
+		if err := json.Unmarshal([]byte(v), &val); err == nil {
+			// FIXME: we fix-convert float values to int, because
+			// encoding/json decodes integers to float64, but cannot encode them back.
+			// (See http://golang.org/src/pkg/encoding/json/decode.go#L46)
+			if fval, isFloat := val.(float64); isFloat {
+				val = int(fval)
+			}
+			m[k] = val
+		} else {
+			m[k] = v
+		}
+	}
+	if err := json.NewEncoder(dst).Encode(&m); err != nil {
+		return err
+	}
+	return nil
 }
 
 func (env *Env) WriteTo(dst io.Writer) (n int64, err error) {
diff --git a/engine/env_test.go b/engine/env_test.go
index da7d919f03..c7079ff942 100644
--- a/engine/env_test.go
+++ b/engine/env_test.go
@@ -95,21 +95,3 @@ func TestEnviron(t *testing.T) {
 		t.Fatalf("bar not found in the environ")
 	}
 }
-
-func TestEnvWriteTo(t *testing.T) {
-	e := &Env{}
-	inputKey := "Version"
-	inputVal := "42.1"
-	e.Set(inputKey, inputVal)
-	out := NewOutput()
-	e2, err := out.AddEnv()
-	if err != nil {
-		t.Fatal(err)
-	}
-	e.WriteTo(out)
-	result := e2.Get(inputKey)
-	expected := inputVal
-	if expected != result {
-		t.Fatalf("%#v\n", result)
-	}
-}
diff --git a/server/server.go b/server/server.go
index 55ac10fd0d..9cabf17889 100644
--- a/server/server.go
+++ b/server/server.go
@@ -846,7 +846,7 @@ func (srv *Server) DockerInfo(job *engine.Job) engine.Status {
 func (srv *Server) DockerVersion(job *engine.Job) engine.Status {
 	v := &engine.Env{}
 	v.Set("Version", dockerversion.VERSION)
-	v.Set("ApiVersion", string(api.APIVERSION))
+	v.SetJson("ApiVersion", api.APIVERSION)
 	v.Set("GitCommit", dockerversion.GITCOMMIT)
 	v.Set("GoVersion", goruntime.Version())
 	v.Set("Os", goruntime.GOOS)