diff --git a/parser/parser.go b/parser/parser.go
index dee4e25..46a1c7d 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -880,9 +880,6 @@ func (p *parser) parseTagValue(ctx *context, tagRawTk *token.Token, tk *Token) (
 		}
 		return p.parseSequence(ctx)
 	}
-	if strings.HasPrefix(tagRawTk.Value, "!!") {
-		return nil, errors.ErrSyntax(fmt.Sprintf("unknown secondary tag name %q specified", tagRawTk.Value), tagRawTk)
-	}
 	return p.parseToken(ctx, tk)
 }
 
diff --git a/parser/parser_test.go b/parser/parser_test.go
index 8d1db7b..c82adb7 100644
--- a/parser/parser_test.go
+++ b/parser/parser_test.go
@@ -70,6 +70,7 @@ func TestParser(t *testing.T) {
 		"%YAML 1.2\n---\n",
 		"a: !!binary gIGC\n",
 		"a: !!binary |\n  " + strings.Repeat("kJCQ", 17) + "kJ\n  CQ\n",
+		"v: !!foo 1",
 		"v:\n- A\n- |-\n  B\n  C\n",
 		"v:\n- A\n- >-\n  B\n  C\n",
 		"v: |-\n  0\n",
@@ -1029,14 +1030,6 @@ func TestSyntaxError(t *testing.T) {
 		source string
 		expect string
 	}{
-		{
-			`v: !!int64 2`,
-			`
-[1:4] unknown secondary tag name "!!int64" specified
->  1 | v: !!int64 2
-          ^
-`,
-		},
 		{
 			`
 a: