diff --git a/src/google/adk/tools/openapi_tool/openapi_spec_parser/rest_api_tool.py b/src/google/adk/tools/openapi_tool/openapi_spec_parser/rest_api_tool.py
index 18dbb70b259..b423e07a021 100644
--- a/src/google/adk/tools/openapi_tool/openapi_spec_parser/rest_api_tool.py
+++ b/src/google/adk/tools/openapi_tool/openapi_spec_parser/rest_api_tool.py
@@ -59,6 +59,7 @@
 from ..auth.auth_helpers import credential_to_param
 from ..auth.auth_helpers import dict_to_auth_scheme
 from ..auth.credential_exchangers.auto_auth_credential_exchanger import AutoAuthCredentialExchanger
+from ..common.common import _schema_from_openapi
 from ..common.common import ApiParameter
 from .openapi_spec_parser import OperationEndpoint
 from .openapi_spec_parser import ParsedOperation
@@ -570,7 +571,14 @@ def _prepare_request_params(
     request_body = self.operation.requestBody
     if request_body:
       for mime_type, media_type_object in request_body.content.items():
-        schema = media_type_object.schema_
+        # Normalized exactly as OperationParser did when it built the body
+        # parameters, so a media type declared without a schema (e.g.
+        # `application/octet-stream: {}`) gets the same single body parameter
+        # instead of crashing here.
+        schema = _schema_from_openapi(
+            media_type_object.schema_,
+            context=f"request body media type {mime_type!r}",
+        )
         body_data = None
 
         if schema.type == "object":
diff --git a/tests/unittests/tools/openapi_tool/openapi_spec_parser/test_rest_api_tool.py b/tests/unittests/tools/openapi_tool/openapi_spec_parser/test_rest_api_tool.py
index 74d6cefd4f4..e61ad3e66ba 100644
--- a/tests/unittests/tools/openapi_tool/openapi_spec_parser/test_rest_api_tool.py
+++ b/tests/unittests/tools/openapi_tool/openapi_spec_parser/test_rest_api_tool.py
@@ -2253,6 +2253,33 @@ def test_prepare_request_params_octet_stream(
         request_params["headers"]["Content-Type"] == "application/octet-stream"
     )
 
+  def test_prepare_request_params_media_type_without_schema(
+      self, sample_endpoint, sample_auth_scheme, sample_auth_credential
+  ):
+    """A media type with no schema gets the parser's single body parameter."""
+    mock_operation = Operation(
+        operationId="upload_contract",
+        requestBody=RequestBody(
+            content={"application/octet-stream": MediaType()}
+        ),
+    )
+    tool = RestApiTool(
+        name="upload_contract",
+        description="test",
+        endpoint=sample_endpoint,
+        operation=mock_operation,
+        auth_credential=sample_auth_credential,
+        auth_scheme=sample_auth_scheme,
+    )
+    params = OperationParser(mock_operation).get_parameters()
+
+    request_params = tool._prepare_request_params(params, {"body": b"%PDF-1.7"})
+
+    assert request_params["data"] == b"%PDF-1.7"
+    assert (
+        request_params["headers"]["Content-Type"] == "application/octet-stream"
+    )
+
   def test_prepare_request_params_path_param(
       self, sample_endpoint, sample_auth_credential, sample_auth_scheme
   ):