diff --git a/litellm/litellm_core_utils/prompt_templates/factory.py b/litellm/litellm_core_utils/prompt_templates/factory.py
index 4990c7081b7..51e8dc6b69c 100644
--- a/litellm/litellm_core_utils/prompt_templates/factory.py
+++ b/litellm/litellm_core_utils/prompt_templates/factory.py
@@ -4739,6 +4739,12 @@ class BedrockConverseMessagesProcessor:
         {"type": "document", "source": {"type": "base64", "media_type": "application/pdf", "data": "..."}}
         """
         source = element["source"]
+        source_type = source.get("type")
+        if source_type != "base64":
+            raise ValueError(
+                f"Bedrock Converse only supports base64-encoded document sources, got '{source_type}'. "
+                "Please convert the document to base64 before sending to Bedrock."
+            )
         media_type: str = source["media_type"]
         data: str = source["data"]
         doc_format = BedrockImageProcessor._validate_format(
diff --git a/tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_factory.py b/tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_factory.py
index 462d697e0a3..27686162f70 100644
--- a/tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_factory.py
+++ b/tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_factory.py
@@ -2508,3 +2508,26 @@ def test_bedrock_converse_messages_pt_document_deterministic_name():
     name1 = result1[0]["content"][0]["document"]["name"]
     name2 = result2[0]["content"][0]["document"]["name"]
     assert name1 == name2
+
+
+def test_bedrock_converse_messages_pt_document_rejects_url_source():
+    """Test that a URL-type document source raises a clear error instead of KeyError."""
+    messages = [
+        {
+            "role": "user",
+            "content": [
+                {
+                    "type": "document",
+                    "source": {
+                        "type": "url",
+                        "url": "https://example.com/doc.pdf",
+                    },
+                },
+            ],
+        }
+    ]
+
+    with pytest.raises(ValueError, match="only supports base64-encoded"):
+        _bedrock_converse_messages_pt(
+            messages, "anthropic.claude-sonnet-4-6", "bedrock"
+        )