diff --git a/models/models_methods.go b/models/models_methods.go
index 66fbf198..8ba9b582 100644
--- a/models/models_methods.go
+++ b/models/models_methods.go
@@ -223,7 +223,11 @@ func (env *EnvironmentItemModel) Normalize() error {
 	return nil
 }
 
-// Normalize ...
+// Normalize - if successful this makes the model JSON serializable.
+// Without this, if the object was created with e.g. a YAML parser,
+// the type of `opts` might be map[interface]interface, which is not JSON serializable.
+// After this call it's ensured that the type of objects is map[string]interface,
+// which is JSON serializable.
 func (envsSerializeObj *EnvsSerializeModel) Normalize() error {
 	for _, envObj := range envsSerializeObj.Envs {
 		if err := envObj.Normalize(); err != nil {
diff --git a/models/models_methods_test.go b/models/models_methods_test.go
index f6e1d4cb..3889dff1 100644
--- a/models/models_methods_test.go
+++ b/models/models_methods_test.go
@@ -3,6 +3,10 @@ package models
 import (
 	"testing"
 
+	yaml "gopkg.in/yaml.v2"
+
+	"encoding/json"
+
 	"github.com/bitrise-io/go-utils/pointers"
 	"github.com/stretchr/testify/require"
 )
@@ -359,3 +363,33 @@ func TestValidate(t *testing.T) {
 	}
 	require.NoError(t, env.Validate())
 }
+
+func Test_EnvsSerializeModel_Normalize(t *testing.T) {
+	yamlContent := `envs:
+- KEY_ONE: first value
+- KEY_TWO: second value, with options
+  opts:
+    is_expand: true
+`
+	var objFromYAML EnvsSerializeModel
+	require.NoError(t, yaml.Unmarshal([]byte(yamlContent), &objFromYAML))
+
+	// the objFromYAML object in this state can't be serialized to JSON directly,
+	// as the YAML parser parses the `opts` into map[interface]interface,
+	// which is not supported by JSON
+	{
+		_, err := json.Marshal(objFromYAML)
+		require.EqualError(t, err, `json: unsupported type: map[interface {}]interface {}`)
+	}
+
+	// now, if we call Normalize on this object, that will convert the map[interface]interface
+	// into map[string]interface, which is JSON serializable
+	require.NoError(t, objFromYAML.Normalize())
+
+	// let's try the serialization again - this time it will work!
+	{
+		jsonContBytes, err := json.Marshal(objFromYAML)
+		require.NoError(t, err)
+		require.Equal(t, `{"envs":[{"KEY_ONE":"first value","opts":{}},{"KEY_TWO":"second value, with options","opts":{"is_expand":true}}]}`, string(jsonContBytes))
+	}
+}