diff --git a/mapper.go b/mapper.go
index dcbacd0..e37ca27 100644
--- a/mapper.go
+++ b/mapper.go
@@ -234,9 +234,6 @@ func mapDecoder(d *Registry) MapperFunc {
 		}
 		el := target.Type()
 		sep := ctx.Value.Tag.Sep
-		if sep == 0 {
-			sep = '='
-		}
 		token := ctx.Scan.PopValue("map")
 		parts := SplitEscaped(token, sep)
 		if len(parts) != 2 {
@@ -267,9 +264,6 @@ func sliceDecoder(d *Registry) MapperFunc {
 	return func(ctx *DecodeContext, target reflect.Value) error {
 		el := target.Type().Elem()
 		sep := ctx.Value.Tag.Sep
-		if sep == 0 {
-			sep = ','
-		}
 		var childScanner *Scanner
 		if ctx.Value.Flag != nil {
 			// If decoding a flag, we need an argument.
diff --git a/resolver.go b/resolver.go
index fd5a02d..5c89a18 100755
--- a/resolver.go
+++ b/resolver.go
@@ -27,9 +27,6 @@ func JSON(r io.Reader) (ResolverFunc, error) {
 			return "", nil
 		}
 		sep := flag.Tag.Sep
-		if sep == 0 {
-			sep = ','
-		}
 		value, err := jsonDecodeValue(sep, raw)
 		if err != nil {
 			return "", err
diff --git a/tag.go b/tag.go
index 1573806..1351471 100644
--- a/tag.go
+++ b/tag.go
@@ -130,6 +130,13 @@ func parseTag(fv reflect.Value, ft reflect.StructField) *Tag {
 	t.Hidden = t.Has("hidden")
 	t.Format, _ = t.Get("format")
 	t.Sep, _ = t.GetRune("sep")
+	if t.Sep == 0 {
+		if fv.Kind() == reflect.Map {
+			t.Sep = '='
+		} else {
+			t.Sep = ','
+		}
+	}
 	t.PlaceHolder, _ = t.Get("placeholder")
 	if t.PlaceHolder == "" {
 		t.PlaceHolder = strings.ToUpper(dashedString(fv.Type().Name()))