diff --git a/litellm/llms/bedrock/common_utils.py b/litellm/llms/bedrock/common_utils.py
index c5ef78b44f3..d18cb7d8734 100644
--- a/litellm/llms/bedrock/common_utils.py
+++ b/litellm/llms/bedrock/common_utils.py
@@ -1314,11 +1314,11 @@ def resolve_s3_encryption_key_id(
     Precedence: `s3_encryption_key_id` in litellm_params, then optional_params
     (client-side / request params), then the AWS_S3_ENCRYPTION_KEY_ID env var.
     """
-    for source in (litellm_params, optional_params or {}):
-        value = source.get("s3_encryption_key_id")
-        if isinstance(value, str) and value:
-            return value
-    return get_secret_str("AWS_S3_ENCRYPTION_KEY_ID")
+    candidates: Final = tuple(
+        source.get("s3_encryption_key_id") for source in (litellm_params, optional_params) if source is not None
+    )
+    explicit: Final = next((value for value in candidates if isinstance(value, str) and value), None)
+    return explicit or get_secret_str("AWS_S3_ENCRYPTION_KEY_ID")
 
 
 class CommonBatchFilesUtils:
diff --git a/litellm/llms/bedrock/files/transformation.py b/litellm/llms/bedrock/files/transformation.py
index b4c4a270bd7..728fd02f001 100644
--- a/litellm/llms/bedrock/files/transformation.py
+++ b/litellm/llms/bedrock/files/transformation.py
@@ -788,20 +788,24 @@ class BedrockFilesConfig(BaseAWSLLM, BaseFilesConfig):
 
         # Prepare headers with required S3 headers (same as s3_v2.py)
         sse_headers: Final = (
-            {
-                "x-amz-server-side-encryption": "aws:kms",
-                "x-amz-server-side-encryption-aws-kms-key-id": s3_encryption_key_id,
-            }
+            MappingProxyType(
+                {
+                    "x-amz-server-side-encryption": "aws:kms",
+                    "x-amz-server-side-encryption-aws-kms-key-id": s3_encryption_key_id,
+                }
+            )
             if s3_encryption_key_id
-            else {}
+            else MappingProxyType({})
+        )
+        request_headers: Final = MappingProxyType(
+            {
+                "Content-Type": "application/json",  # JSONL files are JSON content
+                "x-amz-content-sha256": content_hash,  # REQUIRED by S3
+                "Content-Language": "en",
+                "Cache-Control": "private, immutable, max-age=31536000, s-maxage=0",
+                **sse_headers,
+            }
         )
-        request_headers: Final = {
-            "Content-Type": "application/json",  # JSONL files are JSON content
-            "x-amz-content-sha256": content_hash,  # REQUIRED by S3
-            "Content-Language": "en",
-            "Cache-Control": "private, immutable, max-age=31536000, s-maxage=0",
-            **sse_headers,
-        }
 
         # Use requests.Request to prepare the request (same pattern as s3_v2.py)
         req: Final = requests.Request("PUT", api_base, data=content, headers=request_headers)