diff --git a/core/src/main/java/com/alibaba/fastjson2/JSONReader.java b/core/src/main/java/com/alibaba/fastjson2/JSONReader.java
index 74a93abb7..2b8ff97d3 100644
--- a/core/src/main/java/com/alibaba/fastjson2/JSONReader.java
+++ b/core/src/main/java/com/alibaba/fastjson2/JSONReader.java
@@ -3240,7 +3240,7 @@ protected final String toString(Map object) {
 
     public static JSONReader of(byte[] utf8Bytes) {
         Context context = createReadContext();
-        if (PREDICATE_IS_ASCII.test(utf8Bytes)) {
+        if (PREDICATE_IS_ASCII != null && PREDICATE_IS_ASCII.test(utf8Bytes)) {
             return new JSONReaderASCII(context, null, utf8Bytes, 0, utf8Bytes.length);
         }
 
@@ -3249,7 +3249,7 @@ public static JSONReader of(byte[] utf8Bytes) {
 
     @Deprecated
     public static JSONReader of(Context context, byte[] utf8Bytes) {
-        if (PREDICATE_IS_ASCII.test(utf8Bytes)) {
+        if (PREDICATE_IS_ASCII != null && PREDICATE_IS_ASCII.test(utf8Bytes)) {
             return new JSONReaderASCII(context, null, utf8Bytes, 0, utf8Bytes.length);
         }
 
@@ -3257,7 +3257,7 @@ public static JSONReader of(Context context, byte[] utf8Bytes) {
     }
 
     public static JSONReader of(byte[] utf8Bytes, Context context) {
-        if (PREDICATE_IS_ASCII.test(utf8Bytes)) {
+        if (PREDICATE_IS_ASCII != null && PREDICATE_IS_ASCII.test(utf8Bytes)) {
             return new JSONReaderASCII(context, null, utf8Bytes, 0, utf8Bytes.length);
         }
 
@@ -3500,7 +3500,7 @@ public static JSONReader of(String str) {
                 int coder = STRING_CODER.applyAsInt(str);
                 if (coder == LATIN1) {
                     byte[] bytes = STRING_VALUE.apply(str);
-                    if (PREDICATE_IS_ASCII.test(bytes)) {
+                    if (PREDICATE_IS_ASCII != null && PREDICATE_IS_ASCII.test(bytes)) {
                         return new JSONReaderASCII(context, str, bytes, 0, bytes.length);
                     }
                 }
diff --git a/core/src/main/java/com/alibaba/fastjson2/util/JDKUtils.java b/core/src/main/java/com/alibaba/fastjson2/util/JDKUtils.java
index a8703043d..8d6f8db5a 100644
--- a/core/src/main/java/com/alibaba/fastjson2/util/JDKUtils.java
+++ b/core/src/main/java/com/alibaba/fastjson2/util/JDKUtils.java
@@ -317,9 +317,6 @@ public class JDKUtils {
                     initErrorLast = e;
                 }
             }
-            if (isAscii == null) {
-                isAscii = JDKUtils::isASCII;
-            }
 
             PREDICATE_IS_ASCII = isAscii;
         }
@@ -525,8 +522,4 @@ public static String latin1StringJDK8(byte[] bytes, int offset, int strlen) {
         }
         return STRING_CREATOR_JDK8.apply(chars, Boolean.TRUE);
     }
-
-    static boolean isASCII(byte[] chars) {
-        return IOUtils.isASCII(chars, 0, chars.length);
-    }
 }