diff --git a/weixin-java-common/src/main/java/me/chanjar/weixin/common/util/fs/FileUtils.java b/weixin-java-common/src/main/java/me/chanjar/weixin/common/util/fs/FileUtils.java
index 4a267153c6..8419c87d5a 100644
--- a/weixin-java-common/src/main/java/me/chanjar/weixin/common/util/fs/FileUtils.java
+++ b/weixin-java-common/src/main/java/me/chanjar/weixin/common/util/fs/FileUtils.java
@@ -57,13 +57,10 @@ public static File createTmpFile(InputStream inputStream, String name, String ex
    * @return base64编码
    */
   public static String imageToBase64ByStream(InputStream in) {
-    byte[] data = null;
     // 读取图片字节数组
     try {
-      data = new byte[in.available()];
-      in.read(data);
       // 返回Base64编码过的字节数组字符串
-      return Base64.getEncoder().encodeToString(data);
+      return Base64.getEncoder().encodeToString(IOUtils.toByteArray(in));
     } catch (IOException e) {
       e.printStackTrace();
     } finally {
diff --git a/weixin-java-common/src/test/java/me/chanjar/weixin/common/util/fs/FileUtilsTest.java b/weixin-java-common/src/test/java/me/chanjar/weixin/common/util/fs/FileUtilsTest.java
index 5a25fb1493..3ab603e47c 100644
--- a/weixin-java-common/src/test/java/me/chanjar/weixin/common/util/fs/FileUtilsTest.java
+++ b/weixin-java-common/src/test/java/me/chanjar/weixin/common/util/fs/FileUtilsTest.java
@@ -6,8 +6,10 @@
 import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.IOException;
+import java.io.InputStream;
 import java.nio.charset.Charset;
 import java.nio.file.Files;
+import java.util.Base64;
 import java.util.List;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -30,5 +32,31 @@ public void testTestCreateTmpFile() {
 
   @Test
   public void testImageToBase64ByStream() {
+    byte[] original = new byte[5000];
+    for (int i = 0; i < original.length; i++) {
+      original[i] = (byte) (i % 256);
+    }
+    // A stream that returns at most 16 bytes per read() call (like a network stream),
+    // so a single in.read(buffer) does not fill the buffer.
+    InputStream chunked = new InputStream() {
+      private final ByteArrayInputStream delegate = new ByteArrayInputStream(original);
+
+      @Override
+      public int read() {
+        return delegate.read();
+      }
+
+      @Override
+      public int read(byte[] b, int off, int len) {
+        return delegate.read(b, off, Math.min(len, 16));
+      }
+
+      @Override
+      public int available() {
+        return delegate.available();
+      }
+    };
+    String result = FileUtils.imageToBase64ByStream(chunked);
+    assertThat(result).isEqualTo(Base64.getEncoder().encodeToString(original));
   }
 }