diff --git a/src/tool_schemas.py b/src/tool_schemas.py
index 6468f4f45..176657243 100644
--- a/src/tool_schemas.py
+++ b/src/tool_schemas.py
@@ -41,6 +41,7 @@ _REQUIRED_NATIVE_TOOL_ARGS = {
     "write_file": ("path",),
     "edit_file": ("path",),
     "apply_patch": ("patch_text", "patchText", "patch"),
+    "generate_image": ("prompt",),
     "host_shell": ("command",),
 }
 
diff --git a/tests/test_generate_image_native_schema.py b/tests/test_generate_image_native_schema.py
new file mode 100644
index 000000000..a0364090d
--- /dev/null
+++ b/tests/test_generate_image_native_schema.py
@@ -0,0 +1,59 @@
+"""Native image calls must match the server schema and provide a prompt.
+
+A missing prompt must be rejected before the fallback line parser mistakes the
+whole arguments object for the requested image.
+"""
+
+import json
+
+
+def _schemas():
+    import src.agent_tools  # noqa: F401  (tool_schemas <-> agent_tools import cycle)
+    from src.tool_schemas import FUNCTION_TOOL_SCHEMAS
+
+    return {s["function"]["name"]: s["function"] for s in FUNCTION_TOOL_SCHEMAS}
+
+
+def _convert(arguments):
+    import src.agent_tools  # noqa: F401
+    from src.tool_schemas import function_call_to_tool_block
+
+    return function_call_to_tool_block("generate_image", json.dumps(arguments))
+
+
+def test_generate_image_is_offered_to_native_function_calling_models():
+    schemas = _schemas()
+    assert "generate_image" in schemas, (
+        "generate_image has no native schema, so it is filtered out of the tools "
+        "sent to API models even when the selector picks it"
+    )
+    assert schemas["generate_image"]["parameters"]["required"] == ["prompt"]
+
+
+def test_native_call_reaches_the_executor_with_its_arguments_intact():
+    from src.tool_execution import _build_mcp_args
+
+    args = {"prompt": "a cat riding a bicycle", "model": "gpt-image-1",
+            "size": "1024x1024", "quality": "high"}
+    block = _convert(args)
+    assert block is not None and block.tool_type == "generate_image"
+    assert _build_mcp_args("generate_image", block.content) == args
+
+
+def test_call_without_a_prompt_is_rejected_instead_of_drawing_its_own_arguments():
+    """No prompt key means the line parser takes the whole JSON blob as the prompt,
+    so the model gets an image of its own arguments."""
+    assert _convert({"size": "512x512"}) is None
+    assert _convert({}) is None
+    assert _convert({"prompt": "   "}) is None
+
+
+def test_advertised_parameters_are_the_ones_the_image_server_accepts():
+    """Anything the schema advertises but the executor drops is a silent no-op."""
+    from mcp_servers.image_gen_server import list_tools
+    import asyncio
+
+    server_schema = asyncio.run(list_tools())[0].inputSchema
+    assert set(_schemas()["generate_image"]["parameters"]["properties"]) == set(
+        server_schema["properties"]
+    )