diff --git a/filter.go b/filter.go
index 92fb38f..337bddb 100644
--- a/filter.go
+++ b/filter.go
@@ -12,9 +12,11 @@ type Filter struct {
 	Authors StringList
 	Since   *time.Time
 	Until   *time.Time
-	Tags    map[string]StringList
+	Tags    TagMap
 }
 
+type TagMap map[string]StringList
+
 func (eff Filters) Match(event *Event) bool {
 	for _, filter := range eff {
 		if filter.Matches(event) {
diff --git a/filter_aux.go b/filter_aux.go
index 1bf29b1..f4a4ce9 100644
--- a/filter_aux.go
+++ b/filter_aux.go
@@ -20,7 +20,7 @@ func (f *Filter) UnmarshalJSON(payload []byte) error {
 		return fmt.Errorf("filter is not an object")
 	}
 
-	f.Tags = make(map[string]StringList)
+	f.Tags = make(TagMap)
 
 	var visiterr error
 	obj.Visit(func(k []byte, v *fastjson.Value) {
diff --git a/filter_test.go b/filter_test.go
index 7a6c212..0aed216 100644
--- a/filter_test.go
+++ b/filter_test.go
@@ -26,7 +26,7 @@ func TestFilterMarshal(t *testing.T) {
 
 	filterj, err := json.Marshal(Filter{
 		Kinds: IntList{1, 2, 4},
-		Tags:  map[string]StringList{"fruit": {"banana", "mango"}},
+		Tags:  TagMap{"fruit": {"banana", "mango"}},
 		Until: &tm,
 	})
 	if err != nil {
@@ -50,7 +50,7 @@ func TestFilterMatching(t *testing.T) {
 
 	if !(Filter{
 		Kinds: IntList{4, 5},
-		Tags: map[string]StringList{
+		Tags: TagMap{
 			"p": {"ooo"},
 		},
 		IDs: StringList{"prefix"},
@@ -72,8 +72,8 @@ func TestFilterEquality(t *testing.T) {
 	}
 
 	if !FilterEqual(
-		Filter{Kinds: IntList{4, 5}, Tags: map[string]StringList{"letter": {"a", "b"}}},
-		Filter{Kinds: IntList{4, 5}, Tags: map[string]StringList{"letter": {"b", "a"}}},
+		Filter{Kinds: IntList{4, 5}, Tags: TagMap{"letter": {"a", "b"}}},
+		Filter{Kinds: IntList{4, 5}, Tags: TagMap{"letter": {"b", "a"}}},
 	) {
 		t.Error("kind+tags filters should be equal")
 	}
@@ -82,13 +82,13 @@ func TestFilterEquality(t *testing.T) {
 	if !FilterEqual(
 		Filter{
 			Kinds: IntList{4, 5},
-			Tags:  map[string]StringList{"letter": {"a", "b"}, "fruit": {"banana"}},
+			Tags:  TagMap{"letter": {"a", "b"}, "fruit": {"banana"}},
 			Since: &tm,
 			IDs:   StringList{"aaaa", "bbbb"},
 		},
 		Filter{
 			Kinds: IntList{5, 4},
-			Tags:  map[string]StringList{"letter": {"a", "b"}, "fruit": {"banana"}},
+			Tags:  TagMap{"letter": {"a", "b"}, "fruit": {"banana"}},
 			Since: &tm,
 			IDs:   StringList{"aaaa", "bbbb"},
 		},