diff --git a/.env.example b/.env.example
index 2b4cd8d3..3f7a4531 100644
--- a/.env.example
+++ b/.env.example
@@ -23,8 +23,8 @@ SMTP_REJECT_UNAUTHORIZED= # set to "false" to accept invalid certs
 NEXT_PUBLIC_DISABLE_EMAIL=
 
 # S3 storage (optional)
-S3_REGION=
-S3_ENDPOINT=
+S3_REGION= # required for AWS S3 (e.g. us-east-1); ignored by most S3-compatible providers — defaults to us-east-1 if unset
+S3_ENDPOINT= # set for S3-compatible providers (MinIO, R2, Spaces, etc.); leave blank for AWS S3
 S3_ACCESS_KEY_ID=
 S3_SECRET_ACCESS_KEY=
 S3_FORCE_PATH_STYLE=
diff --git a/packages/shared/src/utils/s3.ts b/packages/shared/src/utils/s3.ts
index a90fb885..5a64043b 100644
--- a/packages/shared/src/utils/s3.ts
+++ b/packages/shared/src/utils/s3.ts
@@ -16,8 +16,14 @@ export function createS3Client() {
         }
       : undefined;
 
+  // The AWS SDK throws "Region is missing" if region is undefined or
+  // empty string at S3Client construction. Default to "us-east-1" so
+  // S3-compatible providers (MinIO, Backblaze B2, R2, Spaces, Wasabi)
+  // that don't care about region work without forcing operators to
+  // set a meaningless value. Real AWS S3 users should still set
+  // S3_REGION explicitly to their bucket's actual region.
   return new S3Client({
-    region: process.env.S3_REGION ?? "",
+    region: process.env.S3_REGION ?? "us-east-1",
     endpoint: process.env.S3_ENDPOINT ?? "",
     forcePathStyle: process.env.S3_FORCE_PATH_STYLE === "true",
     credentials,