diff --git a/keywords.go b/keywords.go
index 66c5eb5..f8467ad 100644
--- a/keywords.go
+++ b/keywords.go
@@ -22,21 +22,24 @@ var primitiveTypes = map[string]bool{
 // DataType gives the primitive json type of a standard json-decoded value, plus the special case
 // "integer" for when numbers are whole
 func DataType(data interface{}) string {
-	switch v := data.(type) {
-	case nil:
+	if data == nil {
 		return "null"
-	case bool:
+	}
+
+	switch reflect.TypeOf(data).Kind() {
+	case reflect.Bool:
 		return "boolean"
-	case float64:
-		if float64(int(v)) == v {
+	case reflect.Float64:
+		number := reflect.ValueOf(data).Float()
+		if float64(int(number)) == number {
 			return "integer"
 		}
 		return "number"
-	case string:
+	case reflect.String:
 		return "string"
-	case []interface{}:
+	case reflect.Array, reflect.Slice:
 		return "array"
-	case map[string]interface{}:
+	case reflect.Map, reflect.Struct:
 		return "object"
 	default:
 		return "unknown"
diff --git a/schema_test.go b/schema_test.go
index cecad8d..32dfed7 100644
--- a/schema_test.go
+++ b/schema_test.go
@@ -449,17 +449,24 @@ func runJSONTests(t *testing.T, testFilepaths []string) {
 }
 
 func TestDataType(t *testing.T) {
+	type customObject struct {}
+	type customNumber float64
+
 	cases := []struct {
 		data   interface{}
 		expect string
 	}{
 		{nil, "null"},
-		{struct{}{}, "unknown"},
 		{float64(4), "integer"},
 		{float64(4.5), "number"},
+		{customNumber(4.5), "number"},
 		{"foo", "string"},
-		{map[string]interface{}{}, "object"},
 		{[]interface{}{}, "array"},
+		{[0]interface{}{}, "array"},
+		{map[string]interface{}{}, "object"},
+		{struct{}{}, "object"},
+		{customObject{}, "object"},
+		{int8(42), "unknown"},
 	}
 
 	for i, c := range cases {