diff --git a/scripts/fetch_dependencies.ps1 b/scripts/fetch_dependencies.ps1
index dbcf507..bc41682 100644
--- a/scripts/fetch_dependencies.ps1
+++ b/scripts/fetch_dependencies.ps1
@@ -14,9 +14,16 @@ Set-Location $ExternalDir
 $OpenJTalkVersion = "1.11"
 $HTSEngineVersion = "1.10"
 
-# Expected SHA256 checksums (update these when upgrading versions)
-$HTSEngineSHA256 = "e2132be5860d8fb4a460be766454cfd7c3e21cf67b509c48e1804feab14968f7"
-$OpenJTalkSHA256 = "20fdc6aeb6c757866034abc175820573db43e4284707c866fcd02c8ec18de71f"
+# GitHub Release mirror for stable downloads (SourceForge hashes can change due to CDN re-compression)
+$GitHubMirrorBase = "https://github.com/ayutaz/openjtalk-native/releases/download/deps-v1"
+
+# SHA256 checksums of .tar.gz files hosted on GitHub Release (stable)
+$HTSEngineGzSHA256 = "e2132be5860d8fb4a460be766454cfd7c3e21cf67b509c48e1804feab14968f7"
+$OpenJTalkGzSHA256 = "20fdc6aeb6c757866034abc175820573db43e4284707c866fcd02c8ec18de71f"
+
+# SHA256 checksums of inner tar content (stable across gzip re-compression)
+$HTSEngineTarSHA256 = "d2924c144f3463b0caea21b6e03cd1573f945652e71f6f221642699e3acec1ff"
+$OpenJTalkTarSHA256 = "1c80e8478e0fa8b8d19e404c897d943d1c496aa84862bf60f58c100c30dd4804"
 
 function Verify-Checksum {
     param(
@@ -31,16 +38,62 @@ function Verify-Checksum {
 
     $actualHash = (Get-FileHash -Path $FilePath -Algorithm SHA256).Hash.ToLower()
     if ($actualHash -ne $ExpectedHash) {
-        Write-Host "ERROR: Checksum mismatch for $FilePath"
+        Write-Host "WARNING: Archive checksum mismatch for $FilePath (may be due to SourceForge re-compression)"
         Write-Host "  Expected: $ExpectedHash"
         Write-Host "  Actual:   $actualHash"
-        Remove-Item $FilePath -Force
         return $false
     }
     Write-Host "Checksum verified for $FilePath"
     return $true
 }
 
+function Verify-GzipFormat {
+    param([string]$FilePath)
+
+    $bytes = [System.IO.File]::ReadAllBytes($FilePath)
+    if ($bytes.Length -lt 2 -or $bytes[0] -ne 0x1F -or $bytes[1] -ne 0x8B) {
+        Write-Host "ERROR: $FilePath is not a valid gzip file"
+        Remove-Item $FilePath -Force
+        return $false
+    }
+    return $true
+}
+
+function Verify-TarChecksum {
+    param(
+        [string]$FilePath,
+        [string]$ExpectedHash
+    )
+
+    if ([string]::IsNullOrEmpty($ExpectedHash)) {
+        Write-Host "WARNING: No inner tar checksum provided, skipping for $FilePath"
+        return $true
+    }
+
+    try {
+        $inStream = [System.IO.File]::OpenRead($FilePath)
+        $gzStream = New-Object System.IO.Compression.GZipStream($inStream, [System.IO.Compression.CompressionMode]::Decompress)
+        $sha256 = [System.Security.Cryptography.SHA256]::Create()
+        $hashBytes = $sha256.ComputeHash($gzStream)
+        $gzStream.Close()
+        $inStream.Close()
+        $actualHash = -join ($hashBytes | ForEach-Object { $_.ToString("x2") })
+
+        if ($actualHash -ne $ExpectedHash) {
+            Write-Host "ERROR: Inner tar checksum mismatch for $FilePath"
+            Write-Host "  Expected: $ExpectedHash"
+            Write-Host "  Actual:   $actualHash"
+            Remove-Item $FilePath -Force
+            return $false
+        }
+        Write-Host "Inner tar checksum verified for $FilePath"
+        return $true
+    } catch {
+        Write-Host "WARNING: Failed to verify inner tar checksum: $_"
+        return $true
+    }
+}
+
 function Download-WithRetry {
     param(
         [string]$Url,
@@ -66,6 +119,27 @@ function Download-WithRetry {
     return $false
 }
 
+function Download-WithFallback {
+    param(
+        [string]$PrimaryUrl,
+        [string]$FallbackUrl,
+        [string]$Output
+    )
+
+    Write-Host "Trying primary mirror (GitHub)..."
+    try {
+        [Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
+        Invoke-WebRequest -Uri $PrimaryUrl -OutFile $Output -UseBasicParsing -TimeoutSec 120
+        Write-Host "Downloaded from GitHub mirror."
+        return $true
+    } catch {
+        Write-Host "Primary mirror unavailable: $_"
+    }
+
+    Write-Host "Trying SourceForge..."
+    return (Download-WithRetry -Url $FallbackUrl -Output $Output)
+}
+
 function Extract-TarGz {
     param([string]$Archive)
 
@@ -88,20 +162,28 @@ Write-Host "=== Fetching OpenJTalk Dependencies ==="
 $HTSDir = "hts_engine_API-$HTSEngineVersion"
 if (-not (Test-Path $HTSDir)) {
     Write-Host "Downloading hts_engine_API $HTSEngineVersion..."
-    $result = Download-WithRetry `
-        -Url "https://sourceforge.net/projects/hts-engine/files/hts_engine%20API/hts_engine_API-$HTSEngineVersion/hts_engine_API-$HTSEngineVersion.tar.gz/download" `
+    $result = Download-WithFallback `
+        -PrimaryUrl "$GitHubMirrorBase/hts_engine_API-$HTSEngineVersion.tar.gz" `
+        -FallbackUrl "https://sourceforge.net/projects/hts-engine/files/hts_engine%20API/hts_engine_API-$HTSEngineVersion/hts_engine_API-$HTSEngineVersion.tar.gz/download" `
         -Output "hts_engine_API.tar.gz"
 
     if (-not $result) {
-        Write-Error "Failed to download hts_engine_API after multiple attempts"
+        Write-Error "Failed to download hts_engine_API"
         exit 1
     }
 
-    if (-not (Verify-Checksum "hts_engine_API.tar.gz" $HTSEngineSHA256)) {
-        Write-Error "Checksum verification failed for hts_engine_API"
+    if (-not (Verify-GzipFormat "hts_engine_API.tar.gz")) {
+        Write-Error "Downloaded hts_engine_API is not a valid gzip file"
         exit 1
     }
 
+    if (-not (Verify-Checksum "hts_engine_API.tar.gz" $HTSEngineGzSHA256)) {
+        if (-not (Verify-TarChecksum "hts_engine_API.tar.gz" $HTSEngineTarSHA256)) {
+            Write-Error "Checksum verification failed for hts_engine_API"
+            exit 1
+        }
+    }
+
     Write-Host "Extracting hts_engine_API..."
     Extract-TarGz "hts_engine_API.tar.gz"
     Remove-Item "hts_engine_API.tar.gz"
@@ -111,20 +193,28 @@ if (-not (Test-Path $HTSDir)) {
 $OJTDir = "open_jtalk-$OpenJTalkVersion"
 if (-not (Test-Path $OJTDir)) {
     Write-Host "Downloading OpenJTalk $OpenJTalkVersion..."
-    $result = Download-WithRetry `
-        -Url "https://sourceforge.net/projects/open-jtalk/files/Open%20JTalk/open_jtalk-$OpenJTalkVersion/open_jtalk-$OpenJTalkVersion.tar.gz/download" `
+    $result = Download-WithFallback `
+        -PrimaryUrl "$GitHubMirrorBase/open_jtalk-$OpenJTalkVersion.tar.gz" `
+        -FallbackUrl "https://sourceforge.net/projects/open-jtalk/files/Open%20JTalk/open_jtalk-$OpenJTalkVersion/open_jtalk-$OpenJTalkVersion.tar.gz/download" `
         -Output "open_jtalk.tar.gz"
 
     if (-not $result) {
-        Write-Error "Failed to download OpenJTalk after multiple attempts"
+        Write-Error "Failed to download OpenJTalk"
         exit 1
     }
 
-    if (-not (Verify-Checksum "open_jtalk.tar.gz" $OpenJTalkSHA256)) {
-        Write-Error "Checksum verification failed for OpenJTalk"
+    if (-not (Verify-GzipFormat "open_jtalk.tar.gz")) {
+        Write-Error "Downloaded OpenJTalk is not a valid gzip file"
         exit 1
     }
 
+    if (-not (Verify-Checksum "open_jtalk.tar.gz" $OpenJTalkGzSHA256)) {
+        if (-not (Verify-TarChecksum "open_jtalk.tar.gz" $OpenJTalkTarSHA256)) {
+            Write-Error "Checksum verification failed for OpenJTalk"
+            exit 1
+        }
+    }
+
     Write-Host "Extracting OpenJTalk..."
     Extract-TarGz "open_jtalk.tar.gz"
     Remove-Item "open_jtalk.tar.gz"
diff --git a/scripts/fetch_dependencies.sh b/scripts/fetch_dependencies.sh
index bbe0a3c..6c69d66 100644
--- a/scripts/fetch_dependencies.sh
+++ b/scripts/fetch_dependencies.sh
@@ -32,6 +32,20 @@ download_with_retry() {
     return 1
 }
 
+download_with_fallback() {
+    local primary_url="$1"
+    local fallback_url="$2"
+    local output="$3"
+
+    echo "Trying primary mirror (GitHub)..."
+    if curl -L --fail --connect-timeout 15 --max-time 120 -o "$output" "$primary_url" 2>/dev/null; then
+        echo "Downloaded from GitHub mirror."
+        return 0
+    fi
+    echo "Primary mirror unavailable, trying SourceForge..."
+    download_with_retry "$fallback_url" "$output"
+}
+
 SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 ROOT_DIR="$(dirname "$SCRIPT_DIR")"
 EXTERNAL_DIR="$ROOT_DIR/external"
@@ -44,9 +58,16 @@ cd "$EXTERNAL_DIR"
 OPENJTALK_VERSION="1.11"
 HTS_ENGINE_VERSION="1.10"
 
-# Expected SHA256 checksums (update these when upgrading versions)
-HTS_ENGINE_SHA256="e2132be5860d8fb4a460be766454cfd7c3e21cf67b509c48e1804feab14968f7"
-OPENJTALK_SHA256="20fdc6aeb6c757866034abc175820573db43e4284707c866fcd02c8ec18de71f"
+# GitHub Release mirror for stable downloads (SourceForge hashes can change due to CDN re-compression)
+GITHUB_MIRROR_BASE="https://github.com/ayutaz/openjtalk-native/releases/download/deps-v1"
+
+# SHA256 checksums of .tar.gz files hosted on GitHub Release (stable)
+HTS_ENGINE_GZ_SHA256="e2132be5860d8fb4a460be766454cfd7c3e21cf67b509c48e1804feab14968f7"
+OPENJTALK_GZ_SHA256="20fdc6aeb6c757866034abc175820573db43e4284707c866fcd02c8ec18de71f"
+
+# SHA256 checksums of inner tar content (stable across gzip re-compression)
+HTS_ENGINE_TAR_SHA256="d2924c144f3463b0caea21b6e03cd1573f945652e71f6f221642699e3acec1ff"
+OPENJTALK_TAR_SHA256="1c80e8478e0fa8b8d19e404c897d943d1c496aa84862bf60f58c100c30dd4804"
 
 verify_checksum() {
     local file="$1"
@@ -65,27 +86,70 @@ verify_checksum() {
         return 0
     fi
     if [ "$actual" != "$expected" ]; then
-        echo "ERROR: Checksum mismatch for $file"
+        echo "WARNING: Archive checksum mismatch for $file (may be due to SourceForge re-compression)"
         echo "  Expected: $expected"
         echo "  Actual:   $actual"
-        rm -f "$file"
         return 1
     fi
     echo "Checksum verified for $file"
     return 0
 }
 
+verify_gzip_format() {
+    local file="$1"
+    local magic
+    magic=$(od -A n -N 2 -t x1 "$file" 2>/dev/null | tr -d ' \n')
+    if [ "$magic" != "1f8b" ]; then
+        echo "ERROR: $file is not a valid gzip file (magic: $magic)"
+        rm -f "$file"
+        return 1
+    fi
+    return 0
+}
+
+verify_tar_checksum() {
+    local file="$1"
+    local expected="$2"
+    if [ -z "$expected" ]; then
+        echo "WARNING: No inner tar checksum provided, skipping for $file"
+        return 0
+    fi
+    local actual
+    if command -v sha256sum >/dev/null 2>&1; then
+        actual=$(gzip -dc "$file" | sha256sum | awk '{print $1}')
+    elif command -v shasum >/dev/null 2>&1; then
+        actual=$(gzip -dc "$file" | shasum -a 256 | awk '{print $1}')
+    else
+        echo "WARNING: No SHA256 tool found, skipping inner tar verification"
+        return 0
+    fi
+    if [ "$actual" != "$expected" ]; then
+        echo "ERROR: Inner tar checksum mismatch for $file"
+        echo "  Expected: $expected"
+        echo "  Actual:   $actual"
+        rm -f "$file"
+        return 1
+    fi
+    echo "Inner tar checksum verified for $file"
+    return 0
+}
+
 echo "=== Fetching OpenJTalk Dependencies ==="
 
 # Download hts_engine_API
 if [ ! -d "hts_engine_API-${HTS_ENGINE_VERSION}" ]; then
     echo "Downloading hts_engine_API ${HTS_ENGINE_VERSION}..."
-    download_with_retry \
+    download_with_fallback \
+        "${GITHUB_MIRROR_BASE}/hts_engine_API-${HTS_ENGINE_VERSION}.tar.gz" \
         "https://sourceforge.net/projects/hts-engine/files/hts_engine%20API/hts_engine_API-${HTS_ENGINE_VERSION}/hts_engine_API-${HTS_ENGINE_VERSION}.tar.gz/download" \
         "hts_engine_API.tar.gz" || \
-        error_exit "Failed to download hts_engine_API after multiple attempts"
+        error_exit "Failed to download hts_engine_API"
 
-    verify_checksum "hts_engine_API.tar.gz" "$HTS_ENGINE_SHA256" || \
+    verify_gzip_format "hts_engine_API.tar.gz" || \
+        error_exit "Downloaded hts_engine_API is not a valid gzip file"
+
+    verify_checksum "hts_engine_API.tar.gz" "$HTS_ENGINE_GZ_SHA256" || \
+        verify_tar_checksum "hts_engine_API.tar.gz" "$HTS_ENGINE_TAR_SHA256" || \
         error_exit "Checksum verification failed for hts_engine_API"
 
     echo "Extracting hts_engine_API..."
@@ -96,12 +160,17 @@ fi
 # Download OpenJTalk
 if [ ! -d "open_jtalk-${OPENJTALK_VERSION}" ]; then
     echo "Downloading OpenJTalk ${OPENJTALK_VERSION}..."
-    download_with_retry \
+    download_with_fallback \
+        "${GITHUB_MIRROR_BASE}/open_jtalk-${OPENJTALK_VERSION}.tar.gz" \
         "https://sourceforge.net/projects/open-jtalk/files/Open%20JTalk/open_jtalk-${OPENJTALK_VERSION}/open_jtalk-${OPENJTALK_VERSION}.tar.gz/download" \
         "open_jtalk.tar.gz" || \
-        error_exit "Failed to download OpenJTalk after multiple attempts"
+        error_exit "Failed to download OpenJTalk"
+
+    verify_gzip_format "open_jtalk.tar.gz" || \
+        error_exit "Downloaded OpenJTalk is not a valid gzip file"
 
-    verify_checksum "open_jtalk.tar.gz" "$OPENJTALK_SHA256" || \
+    verify_checksum "open_jtalk.tar.gz" "$OPENJTALK_GZ_SHA256" || \
+        verify_tar_checksum "open_jtalk.tar.gz" "$OPENJTALK_TAR_SHA256" || \
         error_exit "Checksum verification failed for OpenJTalk"
 
     echo "Extracting OpenJTalk..."