diff --git a/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/modloaders/modpacks/api/ModDownloader.java b/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/modloaders/modpacks/api/ModDownloader.java
index 3b15a2364..f9eb7ee71 100644
--- a/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/modloaders/modpacks/api/ModDownloader.java
+++ b/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/modloaders/modpacks/api/ModDownloader.java
@@ -122,16 +122,14 @@ public class ModDownloader {
                 try {
                     DownloadUtils.ensureSha1(mDestination, mSha1, (Callable<Void>) () -> {
                         IOException exception = tryDownload(sourceUrl);
-
                         if(exception != null) {
-                            downloadFailed(exception);
+                            throw exception;
                         }
-
                         return null;
                     });
 
                 }catch (IOException e) {
-                    return;
+                    downloadFailed(e);
                 }
             }
         }
diff --git a/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/modloaders/modpacks/api/ModpackInstaller.java b/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/modloaders/modpacks/api/ModpackInstaller.java
index 1851b6c27..49b1f6f2f 100644
--- a/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/modloaders/modpacks/api/ModpackInstaller.java
+++ b/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/modloaders/modpacks/api/ModpackInstaller.java
@@ -18,7 +18,7 @@ import java.util.concurrent.Callable;
 
 public class ModpackInstaller {
 
-    public static ModLoader installModpack(ModDetail modDetail, int selectedVersion, InstallFunction installFunction) throws IOException{
+    public static ModLoader installModpack(ModDetail modDetail, int selectedVersion, InstallFunction installFunction) throws IOException {
         String versionUrl = modDetail.versionUrls[selectedVersion];
         String versionHash = modDetail.versionHashes[selectedVersion];
         String modpackName = modDetail.title.toLowerCase(Locale.ROOT).trim().replace(" ", "_" );
diff --git a/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/tasks/NewMinecraftDownloader.java b/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/tasks/NewMinecraftDownloader.java
index 1998176d2..ba9d4da9c 100644
--- a/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/tasks/NewMinecraftDownloader.java
+++ b/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/tasks/NewMinecraftDownloader.java
@@ -16,6 +16,7 @@ import net.kdt.pojavlaunch.JRE17Util;
 import net.kdt.pojavlaunch.R;
 import net.kdt.pojavlaunch.Tools;
 import net.kdt.pojavlaunch.mirrors.DownloadMirror;
+import net.kdt.pojavlaunch.mirrors.MirrorTamperedException;
 import net.kdt.pojavlaunch.prefs.LauncherPreferences;
 import net.kdt.pojavlaunch.utils.DownloadUtils;
 import net.kdt.pojavlaunch.utils.FileUtils;
@@ -34,7 +35,6 @@ import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.atomic.AtomicReference;
 
-// TODO: implement mirror tamper checking.
 public class NewMinecraftDownloader {
     public static final String MINECRAFT_RES = "https://resources.download.minecraft.net/";
     private AtomicReference<Exception> mThrownDownloaderException;
@@ -123,17 +123,22 @@ public class NewMinecraftDownloader {
         return new File(Tools.DIR_HOME_VERSION, versionId + File.separator + versionId + ".jar");
     }
 
-    private File downloadGameJson(JMinecraftVersionList.Version verInfo) throws IOException {
+    private File downloadGameJson(JMinecraftVersionList.Version verInfo) throws IOException, MirrorTamperedException {
         File targetFile = createGameJsonPath(verInfo.id);
         if(verInfo.sha1 == null && targetFile.canRead() && targetFile.isFile())
             return targetFile;
         FileUtils.ensureParentDirectory(targetFile);
-        DownloadUtils.ensureSha1(targetFile, LauncherPreferences.PREF_VERIFY_MANIFEST ? verInfo.sha1 : null, ()-> {
-            ProgressLayout.setProgress(ProgressLayout.DOWNLOAD_MINECRAFT, 0,
-                    R.string.newdl_downloading_metadata, targetFile.getName());
-            DownloadMirror.downloadFileMirrored(DownloadMirror.DOWNLOAD_CLASS_METADATA, verInfo.url, targetFile);
-            return null;
-        });
+        try {
+            DownloadUtils.ensureSha1(targetFile, LauncherPreferences.PREF_VERIFY_MANIFEST ? verInfo.sha1 : null, () -> {
+                ProgressLayout.setProgress(ProgressLayout.DOWNLOAD_MINECRAFT, 0,
+                        R.string.newdl_downloading_metadata, targetFile.getName());
+                DownloadMirror.downloadFileMirrored(DownloadMirror.DOWNLOAD_CLASS_METADATA, verInfo.url, targetFile);
+                return null;
+            });
+        }catch (DownloadUtils.SHA1VerificationException e) {
+            if(DownloadMirror.isMirrored()) throw new MirrorTamperedException();
+            else throw e;
+        }
         return targetFile;
     }
 
@@ -166,7 +171,7 @@ public class NewMinecraftDownloader {
      * @return false if JRE17 installation failed, true otherwise
      * @throws IOException if the download of any of the metadata files fails
      */
-    private boolean downloadAndProcessMetadata(Activity activity, JMinecraftVersionList.Version verInfo, String versionName) throws IOException {
+    private boolean downloadAndProcessMetadata(Activity activity, JMinecraftVersionList.Version verInfo, String versionName) throws IOException, MirrorTamperedException {
         File versionJsonFile;
         if(verInfo != null) versionJsonFile = downloadGameJson(verInfo);
         else versionJsonFile = createGameJsonPath(versionName);
diff --git a/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/utils/DownloadUtils.java b/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/utils/DownloadUtils.java
index 0e281975d..367b415d1 100644
--- a/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/utils/DownloadUtils.java
+++ b/app_pojavlauncher/src/main/java/net/kdt/pojavlaunch/utils/DownloadUtils.java
@@ -120,33 +120,35 @@ public class DownloadUtils {
         return parseResult;
     }
 
+    private static <T> T downloadFile(Callable<T> downloadFunction) throws IOException{
+        try {
+            return downloadFunction.call();
+        } catch (IOException e){
+            throw e;
+        }
+        catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private static boolean verifyFile(File file, String sha1) {
+        return file.exists() && Tools.compareSHA1(file, sha1);
+    }
+
     public static <T> T ensureSha1(File outputFile, @Nullable String sha1, Callable<T> downloadFunction) throws IOException {
         // Skip if needed
-        if(sha1 == null){
-            try {
-                return downloadFunction.call();
-            } catch (IOException e){
-                throw e;
-            }
-            catch (Exception e) {
-                throw new RuntimeException(e);
-            }
-        }
+        if(sha1 == null) return downloadFile(downloadFunction);
 
         int attempts = 0;
+        boolean fileOkay = verifyFile(outputFile, sha1);
         T result = null;
-        while (attempts < 5 && (!outputFile.exists() || !Tools.compareSHA1(outputFile, sha1))){
+        while (attempts < 5 && !fileOkay){
             attempts++;
-            try {
-                result = downloadFunction.call();
-            } catch (IOException e){
-                throw e;
-            } catch (Exception e) {
-                throw new RuntimeException(e);
-            }
+            downloadFile(downloadFunction);
+            fileOkay = verifyFile(outputFile, sha1);
         }
+        if(!fileOkay) throw new SHA1VerificationException("SHA1 verifcation failed after 5 download attempts");
         return result;
-
     }
 
     public interface ParseCallback<T> {
@@ -157,5 +159,11 @@ public class DownloadUtils {
             super(e);
         }
     }
+
+    public static class SHA1VerificationException extends IOException {
+        public SHA1VerificationException(String message) {
+            super(message);
+        }
+    }
 }