diff --git a/core/src/main/java/com/alibaba/fastjson2/JSONReaderUTF16.java b/core/src/main/java/com/alibaba/fastjson2/JSONReaderUTF16.java
index 94232139b3..74c0f370d3 100644
--- a/core/src/main/java/com/alibaba/fastjson2/JSONReaderUTF16.java
+++ b/core/src/main/java/com/alibaba/fastjson2/JSONReaderUTF16.java
@@ -3254,12 +3254,10 @@ public String readString() {
             char[] strBuf = this.strBuf;
             if (strBuf == null) {
                 strBuf = new char[stroff + 512];
-                this.strBuf = strBuf;
             } else if (stroff > strBuf.length) {
-                int newCapacity = newCapacity(stroff, strBuf.length);
-                strBuf = new char[newCapacity];
-                this.strBuf = strBuf;
+                strBuf = new char[newCapacity(stroff, strBuf.length)];
             }
+            this.strBuf = strBuf;
             System.arraycopy(chars, start, strBuf, 0, stroff);
 
             while (true) {
@@ -3272,6 +3270,7 @@ public String readString() {
 
                     if (stroff + 4 >= strBuf.length) {
                         strBuf = Arrays.copyOf(strBuf, newCapacity(stroff + 4, strBuf.length));
+                        this.strBuf = strBuf;
                     }
 
                     IOUtils.putLongLE(strBuf, stroff, v);
@@ -3300,6 +3299,7 @@ public String readString() {
                 }
                 if (stroff == strBuf.length) {
                     strBuf = Arrays.copyOf(strBuf, newCapacity(stroff + 1, strBuf.length));
+                    this.strBuf = strBuf;
                 }
                 strBuf[stroff++] = c;
                 offset++;