diff --git a/internal/encoder/compact.go b/internal/encoder/compact.go
index d70d9e3..4f1bd79 100644
--- a/internal/encoder/compact.go
+++ b/internal/encoder/compact.go
@@ -43,13 +43,32 @@ func Compact(buf *bytes.Buffer, src []byte, escape bool) error {
 }
 
 func compact(dst, src []byte, escape bool) ([]byte, error) {
-	buf, _, err := compactValue(dst, src, 0, escape)
+	buf, cursor, err := compactValue(dst, src, 0, escape)
 	if err != nil {
 		return nil, err
 	}
+	if err := validateEndBuf(src, cursor); err != nil {
+		return nil, err
+	}
 	return buf, nil
 }
 
+func validateEndBuf(src []byte, cursor int64) error {
+	for {
+		switch src[cursor] {
+		case ' ', '\t', '\n', '\r':
+			cursor++
+			continue
+		case nul:
+			return nil
+		}
+		return errors.ErrSyntax(
+			fmt.Sprintf("invalid character '%c' after top-level value", src[cursor]),
+			cursor+1,
+		)
+	}
+}
+
 func skipWhiteSpace(buf []byte, cursor int64) int64 {
 LOOP:
 	if isWhiteSpace[buf[cursor]] {
@@ -90,12 +109,9 @@ func compactValue(dst, src []byte, cursor int64, escape bool) ([]byte, int64, er
 }
 
 func compactObject(dst, src []byte, cursor int64, escape bool) ([]byte, int64, error) {
-	switch src[cursor] {
-	case 'n':
-		return compactNull(dst, src, cursor)
-	case '{':
+	if src[cursor] == '{' {
 		dst = append(dst, '{')
-	default:
+	} else {
 		return nil, 0, errors.ErrExpected("expected { character for object value", cursor)
 	}
 	cursor = skipWhiteSpace(src, cursor+1)
@@ -135,12 +151,9 @@ func compactObject(dst, src []byte, cursor int64, escape bool) ([]byte, int64, e
 }
 
 func compactArray(dst, src []byte, cursor int64, escape bool) ([]byte, int64, error) {
-	switch src[cursor] {
-	case 'n':
-		return compactNull(dst, src, cursor)
-	case '[':
+	if src[cursor] == '[' {
 		dst = append(dst, '[')
-	default:
+	} else {
 		return nil, 0, errors.ErrExpected("expected [ character for array value", cursor)
 	}
 	cursor = skipWhiteSpace(src, cursor+1)
diff --git a/internal/encoder/indent.go b/internal/encoder/indent.go
index 7eed1d8..d593301 100644
--- a/internal/encoder/indent.go
+++ b/internal/encoder/indent.go
@@ -26,10 +26,13 @@ func Indent(buf *bytes.Buffer, src []byte, prefix, indentStr string) error {
 }
 
 func doIndent(dst, src []byte, prefix, indentStr string, escape bool) ([]byte, error) {
-	buf, _, err := indentValue(dst, src, 0, 0, []byte(prefix), []byte(indentStr), escape)
+	buf, cursor, err := indentValue(dst, src, 0, 0, []byte(prefix), []byte(indentStr), escape)
 	if err != nil {
 		return nil, err
 	}
+	if err := validateEndBuf(src, cursor); err != nil {
+		return nil, err
+	}
 	return buf, nil
 }
 
@@ -78,12 +81,9 @@ func indentObject(
 	prefix []byte,
 	indentBytes []byte,
 	escape bool) ([]byte, int64, error) {
-	switch src[cursor] {
-	case 'n':
-		return compactNull(dst, src, cursor)
-	case '{':
+	if src[cursor] == '{' {
 		dst = append(dst, '{')
-	default:
+	} else {
 		return nil, 0, errors.ErrExpected("expected { character for object value", cursor)
 	}
 	cursor = skipWhiteSpace(src, cursor+1)
@@ -139,12 +139,9 @@ func indentArray(
 	prefix []byte,
 	indentBytes []byte,
 	escape bool) ([]byte, int64, error) {
-	switch src[cursor] {
-	case 'n':
-		return compactNull(dst, src, cursor)
-	case '[':
+	if src[cursor] == '[' {
 		dst = append(dst, '[')
-	default:
+	} else {
 		return nil, 0, errors.ErrExpected("expected [ character for array value", cursor)
 	}
 	cursor = skipWhiteSpace(src, cursor+1)
diff --git a/json_test.go b/json_test.go
index 4abac57..47a6c38 100644
--- a/json_test.go
+++ b/json_test.go
@@ -2,6 +2,7 @@ package json_test
 
 import (
 	"bytes"
+	stdjson "encoding/json"
 	"math"
 	"math/rand"
 	"reflect"
@@ -81,9 +82,34 @@ func TestCompact(t *testing.T) {
 		}
 	}
 	t.Run("invalid", func(t *testing.T) {
-		buf.Reset()
-		if err := json.Compact(&buf, []byte(`invalid`)); err == nil {
-			t.Fatal(err)
+		for _, src := range []string{
+			`invalid`,
+			`}`,
+			`]`,
+			`{"a":1}}`,
+			`{"a" 1}`,
+			`{"a": 1 "b": 2}`,
+			`["a" "b"]`,
+			`"\`,
+			`{"a":"\\""}`,
+			`tr`,
+			`{"a": tru, "b": 1}`,
+			`fal`,
+			`{"a": fals, "b": 1}`,
+			`nu`,
+			`{"a": nul, "b": 1}`,
+			`1.234.567`,
+			`[nul]`,
+			`{}   1`,
+		} {
+			buf.Reset()
+			if err := stdjson.Compact(&buf, []byte(src)); err == nil {
+				t.Fatal("invalid test case")
+			}
+			buf.Reset()
+			if err := json.Compact(&buf, []byte(src)); err == nil {
+				t.Fatalf("%q: expected error", src)
+			}
 		}
 	})
 }
@@ -125,6 +151,37 @@ func TestIndent(t *testing.T) {
 			t.Errorf("Indent(%#q) = %#q, want %#q", tt.compact, s, tt.indent)
 		}
 	}
+	t.Run("invalid", func(t *testing.T) {
+		for _, src := range []string{
+			`invalid`,
+			`}`,
+			`]`,
+			`{"a":1}}`,
+			`{"a" 1}`,
+			`{"a": 1 "b": 2}`,
+			`["a" "b"]`,
+			`"\`,
+			`{"a":"\\""}`,
+			`tr`,
+			`{"a": tru, "b": 1}`,
+			`fal`,
+			`{"a": fals, "b": 1}`,
+			`nu`,
+			`{"a": nul, "b": 1}`,
+			`1.234.567`,
+			`[nul]`,
+			`{}   1`,
+		} {
+			buf.Reset()
+			if err := stdjson.Indent(&buf, []byte(src), "", " "); err == nil {
+				t.Fatal("invalid test case")
+			}
+			buf.Reset()
+			if err := json.Indent(&buf, []byte(src), "", " "); err == nil {
+				t.Fatalf("%q: expected error", src)
+			}
+		}
+	})
 }
 
 // Tests of a large random structure.