--- a/vllm/model_executor/layers/quantization/__init__.py
+++ b/vllm/model_executor/layers/quantization/__init__.py
@@ -125,7 +125,13 @@
     from .fp8 import Fp8Config
     from .fp_quant import FPQuantConfig
     from .gguf import GGUFConfig
-    from .humming import HummingConfig
+    try:
+        from .humming import HummingConfig
+    except ImportError:
+        # humming-kernels is optional in this overlay (dev-python/vllm
+        # built with USE=humming); tolerate its absence so the other
+        # quantization methods still resolve.
+        HummingConfig = None
     from .inc import INCConfig
     from .modelopt import (
         ModelOptFp8Config,
@@ -180,7 +186,14 @@
     # Update the `method_to_config` with customized quantization methods.
     method_to_config.update(_CUSTOMIZED_METHOD_TO_QUANT_CONFIG)
 
-    return method_to_config[quantization]
+    config = method_to_config[quantization]
+    if config is None:
+        raise ImportError(
+            f"quantization method {quantization!r} requires "
+            f"dev-python/humming-kernels (rebuild dev-python/vllm "
+            f"with USE=humming)"
+        )
+    return config
 
 
 __all__ = [