diff --git a/gen/encoder.go b/gen/encoder.go
index 5c29a8a..ebd01f8 100644
--- a/gen/encoder.go
+++ b/gen/encoder.go
@@ -290,32 +290,43 @@ func (g *Generator) notEmptyCheck(t reflect.Type, v string) string {
 	}
 }
 
-func (g *Generator) genStructFieldEncoder(t reflect.Type, f reflect.StructField) error {
+func (g *Generator) genStructFieldEncoder(t reflect.Type, f reflect.StructField, first bool) (bool, error) {
 	jsonName := g.fieldNamer.GetJSONFieldName(t, f)
 	tags := parseFieldTags(f)
 
 	if tags.omit {
-		return nil
+		return first, nil
 	}
+
+	toggleFirst := first
+
 	noOmitEmpty := (!tags.omitEmpty && !g.omitEmpty) || tags.noOmitEmpty
 	if noOmitEmpty {
 		fmt.Fprintln(g.out, "  {")
+		toggleFirst = false
 	} else {
 		fmt.Fprintln(g.out, "  if", g.notEmptyCheck(f.Type, "in."+f.Name), "{")
+		// can be any in runtime, so toggleFirst stay as is
+	}
+
+	if first {
+		fmt.Fprintf(g.out, "    const prefix string = %q\n", ","+strconv.Quote(jsonName)+":")
+		fmt.Fprintln(g.out, "    if first {")
+		fmt.Fprintln(g.out, "      first = false")
+		fmt.Fprintln(g.out, "      out.RawString(prefix[1:])")
+		fmt.Fprintln(g.out, "    } else {")
+		fmt.Fprintln(g.out, "      out.RawString(prefix)")
+		fmt.Fprintln(g.out, "    }")
+	} else {
+		fmt.Fprintf(g.out, "    const prefix string = %q\n", ","+strconv.Quote(jsonName)+":")
+		fmt.Fprintln(g.out, "    out.RawString(prefix)")
 	}
-	fmt.Fprintf(g.out, "    const prefix string = %q\n", ","+strconv.Quote(jsonName)+":")
-	fmt.Fprintln(g.out, "    if first {")
-	fmt.Fprintln(g.out, "      first = false")
-	fmt.Fprintln(g.out, "      out.RawString(prefix[1:])")
-	fmt.Fprintln(g.out, "    } else {")
-	fmt.Fprintln(g.out, "      out.RawString(prefix)")
-	fmt.Fprintln(g.out, "    }")
 
 	if err := g.genTypeEncoder(f.Type, "in."+f.Name, tags, 2, !noOmitEmpty); err != nil {
-		return err
+		return toggleFirst, err
 	}
 	fmt.Fprintln(g.out, "  }")
-	return nil
+	return toggleFirst, nil
 }
 
 func (g *Generator) genEncoder(t reflect.Type) error {
@@ -363,8 +374,12 @@ func (g *Generator) genStructEncoder(t reflect.Type) error {
 	if err != nil {
 		return fmt.Errorf("cannot generate encoder for %v: %v", t, err)
 	}
+
+	first := true
 	for _, f := range fs {
-		if err := g.genStructFieldEncoder(t, f); err != nil {
+		first, err = g.genStructFieldEncoder(t, f, first)
+
+		if err != nil {
 			return err
 		}
 	}
diff --git a/gen/generator.go b/gen/generator.go
index 13c54c4..4a8f5a8 100644
--- a/gen/generator.go
+++ b/gen/generator.go
@@ -156,8 +156,9 @@ func (g *Generator) printHeader() {
 	fmt.Println("package ", g.pkgName)
 	fmt.Println()
 
-	byAlias := map[string]string{}
-	var aliases []string
+	byAlias := make(map[string]string, len(g.imports))
+	aliases := make([]string, 0, len(g.imports))
+
 	for path, alias := range g.imports {
 		aliases = append(aliases, alias)
 		byAlias[alias] = path
@@ -388,9 +389,9 @@ func (DefaultFieldNamer) GetJSONFieldName(t reflect.Type, f reflect.StructField)
 	jsonName := strings.Split(f.Tag.Get("json"), ",")[0]
 	if jsonName != "" {
 		return jsonName
-	} else {
-		return f.Name
 	}
+
+	return f.Name
 }
 
 // LowerCamelCaseFieldNamer
@@ -454,9 +455,9 @@ func (LowerCamelCaseFieldNamer) GetJSONFieldName(t reflect.Type, f reflect.Struc
 	jsonName := strings.Split(f.Tag.Get("json"), ",")[0]
 	if jsonName != "" {
 		return jsonName
-	} else {
-		return lowerFirst(f.Name)
 	}
+
+	return lowerFirst(f.Name)
 }
 
 // SnakeCaseFieldNamer implements CamelCase to snake_case conversion for fields names.