diff --git a/app/src/main/java/com/hippo/ehviewer/gallery/DirGalleryProvider.java b/app/src/main/java/com/hippo/ehviewer/gallery/DirGalleryProvider.java
index 8ae1cb9d9..718331891 100644
--- a/app/src/main/java/com/hippo/ehviewer/gallery/DirGalleryProvider.java
+++ b/app/src/main/java/com/hippo/ehviewer/gallery/DirGalleryProvider.java
@@ -106,6 +106,13 @@ public class DirGalleryProvider extends GalleryProvider implements Runnable {
         return mError;
     }
 
+    @NonNull
+    @Override
+    public String getImageFilename(int index) {
+        // TODO
+        return Integer.toString(index);
+    }
+
     @Override
     public boolean save(int index, @NonNull UniFile file) {
         UniFile[] fileList = mFileList.get();
diff --git a/app/src/main/java/com/hippo/ehviewer/gallery/EhGalleryProvider.java b/app/src/main/java/com/hippo/ehviewer/gallery/EhGalleryProvider.java
index d517f6752..15f374ade 100644
--- a/app/src/main/java/com/hippo/ehviewer/gallery/EhGalleryProvider.java
+++ b/app/src/main/java/com/hippo/ehviewer/gallery/EhGalleryProvider.java
@@ -26,6 +26,8 @@ import com.hippo.image.Image;
 import com.hippo.unifile.UniFile;
 import com.hippo.yorozuya.SimpleHandler;
 
+import java.util.Locale;
+
 public class EhGalleryProvider extends GalleryProvider implements SpiderQueen.OnSpiderListener {
 
     private final Context mContext;
@@ -73,6 +75,12 @@ public class EhGalleryProvider extends GalleryProvider implements SpiderQueen.On
         }
     }
 
+    @NonNull
+    @Override
+    public String getImageFilename(int index) {
+        return String.format(Locale.US, "%d-%08d", mGalleryInfo.gid, index + 1);
+    }
+
     @Override
     public boolean save(int index, @NonNull UniFile file) {
         if (null != mSpiderQueen) {
diff --git a/app/src/main/java/com/hippo/ehviewer/gallery/GalleryProvider.java b/app/src/main/java/com/hippo/ehviewer/gallery/GalleryProvider.java
index debaf0148..a4bd336cc 100644
--- a/app/src/main/java/com/hippo/ehviewer/gallery/GalleryProvider.java
+++ b/app/src/main/java/com/hippo/ehviewer/gallery/GalleryProvider.java
@@ -89,6 +89,12 @@ public abstract class GalleryProvider {
         return 0;
     }
 
+    /**
+     * @return without extension
+     */
+    @NonNull
+    public abstract String getImageFilename(int index);
+
     public abstract boolean save(int index, @NonNull UniFile file);
 
     /**
diff --git a/app/src/main/java/com/hippo/ehviewer/gallery/ZipGalleryProvider.java b/app/src/main/java/com/hippo/ehviewer/gallery/ZipGalleryProvider.java
index 1e257da39..97f2f4a37 100644
--- a/app/src/main/java/com/hippo/ehviewer/gallery/ZipGalleryProvider.java
+++ b/app/src/main/java/com/hippo/ehviewer/gallery/ZipGalleryProvider.java
@@ -107,6 +107,13 @@ public class ZipGalleryProvider extends GalleryProvider implements Runnable {
         return mError;
     }
 
+    @NonNull
+    @Override
+    public String getImageFilename(int index) {
+        // TODO
+        return Integer.toString(index);
+    }
+
     @Override
     public boolean save(int index, @NonNull UniFile file) {
         // TODO
diff --git a/app/src/main/java/com/hippo/ehviewer/ui/GalleryActivity.java b/app/src/main/java/com/hippo/ehviewer/ui/GalleryActivity.java
index ece93a8d4..5e76db368 100644
--- a/app/src/main/java/com/hippo/ehviewer/ui/GalleryActivity.java
+++ b/app/src/main/java/com/hippo/ehviewer/ui/GalleryActivity.java
@@ -705,7 +705,7 @@ public class GalleryActivity extends TrackedActivity
             return;
         }
         UniFile file;
-        if (null == (file = mGalleryProvider.save(page, UniFile.fromFile(dir), Long.toString(System.currentTimeMillis())))) {
+        if (null == (file = mGalleryProvider.save(page, UniFile.fromFile(dir), mGalleryProvider.getImageFilename(page)))) {
             Toast.makeText(this, R.string.error_cant_save_image, Toast.LENGTH_SHORT).show();
             return;
         }