diff --git a/backend/routes/models.py b/backend/routes/models.py
index 600e0221..b7533465 100644
--- a/backend/routes/models.py
+++ b/backend/routes/models.py
@@ -59,7 +59,7 @@ def _resolve_model_config(model_name: str):
         known = sorted(cfg.model_name for cfg in get_all_model_configs())
         raise HTTPException(
             status_code=400,
-            detail=f"Unknown model: {model_name}. Available: {known}",
+            detail=f"Unknown model: {model_name!r}. Available: {known}",
         )
     return config
 
@@ -71,10 +71,12 @@ async def load_model(
 ):
     """Load a model into memory.
 
-    Pass ``{"model_name": "kokoro"}`` to target any registered engine. Without
-    a name this falls back to the default Qwen TTS backend, selected by the
-    ``model_size`` query parameter, which is what callers did before
-    ``model_name`` existed.
+    Pass ``{"model_name": "kokoro"}`` to target any registered engine. Only an
+    absent ``model_name`` falls back to the default Qwen TTS backend, selected
+    by the ``model_size`` query parameter, which is what callers did before
+    ``model_name`` existed. A supplied-but-empty name is a bad request, not a
+    request for the default — silently loading Qwen there is the very bug this
+    endpoint had.
     """
     from ..backends import get_model_load_func
     from ..services import tts
@@ -82,7 +84,7 @@ async def load_model(
     requested_name = request.model_name if request else None
     requested_size = (request.model_size if request else None) or model_size
 
-    if requested_name:
+    if requested_name is not None:
         config = _resolve_model_config(requested_name)
         try:
             result = get_model_load_func(config)()
@@ -106,15 +108,16 @@ async def unload_model(request: models.ModelLoadRequest | None = None):
     """Unload a model from memory.
 
     Pass ``{"model_name": "chatterbox-tts"}`` to target a specific engine —
-    same behaviour as ``POST /models/{model_name}/unload``. Without a name
-    this unloads the default Qwen TTS model, as it always has.
+    same behaviour as ``POST /models/{model_name}/unload``. Only an absent
+    ``model_name`` unloads the default Qwen TTS model, as it always has; a
+    supplied-but-empty name is a bad request.
     """
     from ..backends import unload_model_by_config
     from ..services import tts
 
     requested_name = request.model_name if request else None
 
-    if requested_name:
+    if requested_name is not None:
         config = _resolve_model_config(requested_name)
         try:
             was_loaded = unload_model_by_config(config)
diff --git a/backend/tests/test_models_load_by_name.py b/backend/tests/test_models_load_by_name.py
index 4773c76a..1e1f50a3 100644
--- a/backend/tests/test_models_load_by_name.py
+++ b/backend/tests/test_models_load_by_name.py
@@ -96,12 +96,32 @@ def test_load_unknown_model_is_rejected(client, loaded):
     assert loaded["qwen_size"] == []
 
 
+def test_load_empty_model_name_is_rejected(client, loaded):
+    """A supplied-but-empty name is a bad request, not a request for Qwen.
+
+    Falling back here would reproduce #977 in miniature: a caller that named a
+    model (an unbound UI select, say) gets a silent 3.6 GB Qwen download.
+    """
+    response = client.post("/models/load", json={"model_name": ""})
+
+    assert response.status_code == 400
+    assert loaded["by_config"] == []
+    assert loaded["qwen_size"] == []
+
+
 def test_load_without_body_keeps_the_qwen_default(client, loaded):
     """Pre-existing callers post no body at all."""
     assert client.post("/models/load").status_code == 200
     assert loaded["qwen_size"] == ["1.7B"]
 
 
+def test_load_null_model_name_keeps_the_qwen_default(client, loaded):
+    """An explicit null is 'unspecified', unlike an empty string."""
+    assert client.post("/models/load", json={"model_name": None}).status_code == 200
+    assert loaded["qwen_size"] == ["1.7B"]
+    assert loaded["by_config"] == []
+
+
 def test_load_still_honors_the_model_size_query_param(client, loaded):
     """The legacy ?model_size= form must keep selecting the Qwen variant."""
     assert client.post("/models/load?model_size=0.6B").status_code == 200
@@ -121,12 +141,26 @@ def test_unload_by_model_name_targets_that_model(client, loaded):
     assert loaded["qwen_unload"] == 0, "must not unload the default Qwen model instead"
 
 
+def test_unload_empty_model_name_is_rejected(client, loaded):
+    response = client.post("/models/unload", json={"model_name": ""})
+
+    assert response.status_code == 400
+    assert loaded["by_config"] == []
+    assert loaded["qwen_unload"] == 0
+
+
 def test_unload_without_body_keeps_the_qwen_default(client, loaded):
     assert client.post("/models/unload").status_code == 200
     assert loaded["qwen_unload"] == 1
     assert loaded["by_config"] == []
 
 
+def test_unload_null_model_name_keeps_the_qwen_default(client, loaded):
+    assert client.post("/models/unload", json={"model_name": None}).status_code == 200
+    assert loaded["qwen_unload"] == 1
+    assert loaded["by_config"] == []
+
+
 def test_unload_unknown_model_is_rejected(client, loaded):
     response = client.post("/models/unload", json={"model_name": "not-a-model"})