diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index abc9813..72bc3b3 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -732,6 +732,8 @@ jobs:
       AWS_DEFAULT_REGION: ${{ vars.S3_REGION }}
       AWS_REGION: ${{ vars.S3_REGION }}
       AWS_EC2_METADATA_DISABLED: "true"
+      AWS_REQUEST_CHECKSUM_CALCULATION: "WHEN_REQUIRED"
+      AWS_RESPONSE_CHECKSUM_VALIDATION: "WHEN_REQUIRED"
 
     steps:
       - uses: actions/checkout@v4
@@ -806,6 +808,7 @@ jobs:
         shell: bash
         run: |
           set -euo pipefail
+          aws --version
           aws --endpoint-url "$S3_ENDPOINT" --region "$S3_REGION" s3 ls "s3://$S3_BUCKET" >/dev/null
           echo "S3 access probe succeeded for $S3_BUCKET"
 
diff --git a/scripts/Publish-Plonds.ps1 b/scripts/Publish-Plonds.ps1
index 659c449..518a520 100644
--- a/scripts/Publish-Plonds.ps1
+++ b/scripts/Publish-Plonds.ps1
@@ -80,11 +80,36 @@ function Invoke-AwsSyncIfPossible {
         return
     }
 
-    if ($IgnoreFailure) {
-        & aws @Arguments 2>$null
+    $previousRequestChecksumCalculation = $env:AWS_REQUEST_CHECKSUM_CALCULATION
+    $previousResponseChecksumValidation = $env:AWS_RESPONSE_CHECKSUM_VALIDATION
+
+    # Rainyun's S3-compatible endpoint rejects AWS CLI v2's default checksum headers
+    # during multipart uploads. Restrict checksum behavior to API-required cases only.
+    $env:AWS_REQUEST_CHECKSUM_CALCULATION = "WHEN_REQUIRED"
+    $env:AWS_RESPONSE_CHECKSUM_VALIDATION = "WHEN_REQUIRED"
+
+    try {
+        if ($IgnoreFailure) {
+            & aws @Arguments 2>$null
+        }
+        else {
+            & aws @Arguments
+        }
     }
-    else {
-        & aws @Arguments
+    finally {
+        if ($null -eq $previousRequestChecksumCalculation) {
+            Remove-Item Env:AWS_REQUEST_CHECKSUM_CALCULATION -ErrorAction SilentlyContinue
+        }
+        else {
+            $env:AWS_REQUEST_CHECKSUM_CALCULATION = $previousRequestChecksumCalculation
+        }
+
+        if ($null -eq $previousResponseChecksumValidation) {
+            Remove-Item Env:AWS_RESPONSE_CHECKSUM_VALIDATION -ErrorAction SilentlyContinue
+        }
+        else {
+            $env:AWS_RESPONSE_CHECKSUM_VALIDATION = $previousResponseChecksumValidation
+        }
     }
 
     if ($LASTEXITCODE -ne 0 -and -not $IgnoreFailure) {