diff --git a/vskernels/kernels/abstract.py b/vskernels/kernels/abstract.py
index f5f1750..9b55204 100644
--- a/vskernels/kernels/abstract.py
+++ b/vskernels/kernels/abstract.py
@@ -9,7 +9,8 @@
 from vstools import (
     CustomIndexError, CustomRuntimeError, CustomValueError, FieldBased, FuncExceptT, GenericVSFunction,
     HoldsVideoFormatT, KwargsT, Matrix, MatrixT, PropEnum, T, VideoFormatT, check_correct_subsampling,
-    check_variable_resolution, core, depth, expect_bits, get_subclasses, get_video_format, inject_self, vs, vs_object
+    check_variable_resolution, core, depth, expect_bits, fallback, get_subclasses, get_video_format, inject_self, vs,
+    vs_object
 )
 
 from ..exceptions import UnknownDescalerError, UnknownKernelError, UnknownResamplerError, UnknownScalerError
@@ -175,6 +176,10 @@ def __init_subclass__(cls) -> None:
             if mro:
                 raise CustomRuntimeError('You must implement kernel_radius when inheriting BaseScaler!', reason=cls)
 
+    @staticmethod
+    def _wh_norm(clip: vs.VideoNode, width: int | None = None, height: int | None = None) -> tuple[int, int]:
+        return (fallback(width, clip.width), fallback(height, clip.height))
+
     @classmethod
     def from_param(
         cls: type[BaseScalerT], scaler: str | type[BaseScalerT] | BaseScalerT | None = None, /,
@@ -217,8 +222,10 @@ class Scaler(BaseScaler):
     @inject_self.cached
     @inject_kwargs_params
     def scale(  # type: ignore[override]
-        self, clip: vs.VideoNode, width: int, height: int, shift: tuple[TopShift, LeftShift] = (0, 0), **kwargs: Any
+        self, clip: vs.VideoNode, width: int | None = None, height: int | None = None,
+        shift: tuple[TopShift, LeftShift] = (0, 0), **kwargs: Any
     ) -> vs.VideoNode:
+        width, height = Scaler._wh_norm(clip, width, height)
         check_correct_subsampling(clip, width, height)
         return self.scale_function(clip, **_norm_props_enums(self.get_scale_args(clip, shift, width, height, **kwargs)))
 
@@ -270,8 +277,10 @@ class Descaler(BaseScaler):
     @inject_self.cached
     @inject_kwargs_params
     def descale(  # type: ignore[override]
-        self, clip: vs.VideoNode, width: int, height: int, shift: tuple[TopShift, LeftShift] = (0, 0), **kwargs: Any
+        self, clip: vs.VideoNode, width: int | None, height: int | None, shift: tuple[TopShift, LeftShift] = (0, 0), **kwargs: Any
     ) -> vs.VideoNode:
+        width, height = self._wh_norm(clip, width, height)
+
         check_correct_subsampling(clip, width, height)
 
         field_based = FieldBased.from_param_or_video(kwargs.pop('field_based', None), clip)
diff --git a/vskernels/kernels/complex.py b/vskernels/kernels/complex.py
index 39b3af0..44f297a 100644
--- a/vskernels/kernels/complex.py
+++ b/vskernels/kernels/complex.py
@@ -77,7 +77,8 @@ class _BaseLinearOperation:
     def _linear_op(op_name: str) -> Any:
         @inject_kwargs_params
         def func(
-            self: _BaseLinearOperation, clip: vs.VideoNode, width: int, height: int,
+            self: _BaseLinearOperation, clip: vs.VideoNode, width: int | None = None, height: int | None = None,
+
             shift: tuple[TopShift, LeftShift] = (0, 0), *,
             linear: bool = False, sigmoid: bool | tuple[Slope, Center] = False, **kwargs: Any
         ) -> vs.VideoNode:
@@ -110,7 +111,8 @@ class LinearScaler(_BaseLinearOperation, Scaler):
         @inject_self.cached
         @inject_kwargs_params
         def scale(  # type: ignore[override]
-            self, clip: vs.VideoNode, width: int, height: int, shift: tuple[TopShift, LeftShift] = (0, 0),
+            self, clip: vs.VideoNode, width: int | None = None, height: int | None = None, 
+            shift: tuple[TopShift, LeftShift] = (0, 0),
             *, linear: bool = False, sigmoid: bool | tuple[Slope, Center] = False, **kwargs: Any
         ) -> vs.VideoNode:
             ...
@@ -123,7 +125,8 @@ class LinearDescaler(_BaseLinearOperation, Descaler):
         @inject_self.cached
         @inject_kwargs_params
         def descale(  # type: ignore[override]
-            self, clip: vs.VideoNode, width: int, height: int, shift: tuple[TopShift, LeftShift] = (0, 0),
+            self, clip: vs.VideoNode, width: int | None = None, height: int | None = None,
+            shift: tuple[TopShift, LeftShift] = (0, 0),
             *, linear: bool = False, sigmoid: bool | tuple[Slope, Center] = False, **kwargs: Any
         ) -> vs.VideoNode:
             ...
@@ -153,7 +156,7 @@ def _get_kwargs_keep_ar(
         return kwargs
 
     def _handle_crop_resize_kwargs(  # type: ignore[override]
-        self, clip: vs.VideoNode, width: int, height: int, shift: tuple[TopShift, LeftShift],
+        self, clip: vs.VideoNode, width: int | None, height: int | None, shift: tuple[TopShift, LeftShift],
         sar: Sar | bool | float | None, dar: Dar | bool | float | None, **kwargs: Any
     ) -> tuple[KwargsT, tuple[TopShift, LeftShift], Sar | None]:
         kwargs.setdefault('src_top', kwargs.pop('sy', shift[0]))
@@ -199,11 +202,14 @@ def _handle_crop_resize_kwargs(  # type: ignore[override]
     @inject_self.cached
     @inject_kwargs_params
     def scale(  # type: ignore[override]
-        self, clip: vs.VideoNode, width: int, height: int, shift: tuple[TopShift, LeftShift] = (0, 0), *,
+        self, clip: vs.VideoNode, width: int | None = None, height: int | None = None, 
+        shift: tuple[TopShift, LeftShift] = (0, 0), *,
         border_handling: BorderHandling = BorderHandling.MIRROR,
         sar: Sar | float | bool | None = None, dar: Dar | float | bool | None = None, keep_ar: bool = False,
         **kwargs: Any
     ) -> vs.VideoNode:
+        width, height = Scaler._wh_norm(clip, width, height)
+
         check_correct_subsampling(clip, width, height)
 
         const_size = 0 not in (clip.width, clip.height)
@@ -231,13 +237,15 @@ class ComplexScaler(LinearScaler, KeepArScaler):
     @inject_self.cached
     @inject_kwargs_params
     def scale(  # type: ignore[override]
-        self, clip: vs.VideoNode, width: int, height: int, shift: tuple[TopShift, LeftShift] = (0, 0),
+        self, clip: vs.VideoNode, width: int | None = None, height: int | None = None, 
+        shift: tuple[TopShift, LeftShift] = (0, 0),
         *,
         border_handling: BorderHandling = BorderHandling.MIRROR,
         sar: Sar | bool | float | None = None, dar: Dar | bool | float | None = None, keep_ar: bool = False,
         linear: bool = False, sigmoid: bool | tuple[Slope, Center] = False,
         **kwargs: Any
     ) -> vs.VideoNode:
+        width, height = Scaler._wh_norm(clip, width, height)
         return super().scale(
             clip, width, height, shift, sar=sar, dar=dar, keep_ar=keep_ar,
             linear=linear, sigmoid=sigmoid, border_handling=border_handling,
diff --git a/vskernels/kernels/docs.py b/vskernels/kernels/docs.py
index bf5c02d..a6010dc 100644
--- a/vskernels/kernels/docs.py
+++ b/vskernels/kernels/docs.py
@@ -21,7 +21,8 @@ def __init__(self, b: float = 0, c: float = 1 / 2, **kwargs: Any) -> None:
 
     @inject_self.cached
     def scale(  # type: ignore[override]
-        self, clip: vs.VideoNode, width: int, height: int, shift: tuple[float, float] = (0, 0), **kwargs: Any
+        self, clip: vs.VideoNode, width: int | None = None, height: int | None = None,
+        shift: tuple[float, float] = (0, 0), **kwargs: Any
     ) -> vs.VideoNode:
         """
         Perform a regular scaling operation.
@@ -34,6 +35,7 @@ def scale(  # type: ignore[override]
 
         :rtype:             ``VideoNode``
         """
+        width, height = self._wh_norm(clip, width, height)
         return core.resize.Bicubic(
             clip, width, height, src_top=shift[0], src_left=shift[1],
             filter_param_a=self.b, filter_param_b=self.c, **self.kwargs, **kwargs
@@ -41,7 +43,7 @@ def scale(  # type: ignore[override]
 
     @inject_self.cached
     def descale(  # type: ignore[override]
-        self, clip: vs.VideoNode, width: int, height: int, shift: tuple[float, float] = (0, 0), **kwargs: Any
+        self, clip: vs.VideoNode, width: int | None, height: int | None, shift: tuple[float, float] = (0, 0), **kwargs: Any
     ) -> vs.VideoNode:
         """
         Perform a regular descaling operation.
@@ -54,6 +56,7 @@ def descale(  # type: ignore[override]
 
         :rtype:             ``VideoNode``
         """
+        width, height = self._wh_norm(clip, width, height)
         return depth(core.descale.Debicubic(
             depth(clip, 32), width, height, b=self.b, c=self.c, src_top=shift[0], src_left=shift[1], **kwargs
         ), clip)
diff --git a/vskernels/kernels/impulse.py b/vskernels/kernels/impulse.py
index e3388b6..fa7d13d 100644
--- a/vskernels/kernels/impulse.py
+++ b/vskernels/kernels/impulse.py
@@ -44,9 +44,10 @@ def __init__(self, impulse: Sequence[float], oversample: int = 8, taps: float =
     @inject_self.cached
     @inject_kwargs_params
     def scale(  # type: ignore[override]
-        self, clip: vs.VideoNode, width: int, height: int,
+        self, clip: vs.VideoNode, width: int | None = None, height: int | None = None,
         shift: tuple[TopShift, LeftShift] = (-0.125, -0.125), **kwargs: Any
     ) -> vs.VideoNode:
+        width, height = self._wh_norm(clip, width, height)
         return super().scale(clip, width, height, shift, **kwargs)
 
 
diff --git a/vskernels/kernels/placebo.py b/vskernels/kernels/placebo.py
index afc005b..62e42ff 100644
--- a/vskernels/kernels/placebo.py
+++ b/vskernels/kernels/placebo.py
@@ -57,10 +57,11 @@ def __init__(
     @inject_self.cached
     @inject_kwargs_params
     def scale(  # type: ignore[override]
-        self, clip: vs.VideoNode, width: int, height: int, shift: tuple[TopShift, LeftShift] = (0, 0),
-        *, linear: bool = True, sigmoid: bool | tuple[Slope, Center] = True, curve: TransferT | None = None,
-        **kwargs: Any
+        self, clip: vs.VideoNode, width: int | None = None, height: int | None = None,
+        shift: tuple[TopShift, LeftShift] = (0, 0), *,
+        linear: bool = True, sigmoid: bool | tuple[Slope, Center] = True, curve: TransferT | None = None, **kwargs: Any
     ) -> vs.VideoNode:
+        width, height = self._wh_norm(clip, width, height)
         return super().scale(
             clip, width, height, shift, linear=linear, sigmoid=sigmoid,
             trc=Transfer.from_param_or_video(curve, clip).value_libplacebo
diff --git a/vskernels/kernels/zimg.py b/vskernels/kernels/zimg.py
index 7778648..4d21a4d 100644
--- a/vskernels/kernels/zimg.py
+++ b/vskernels/kernels/zimg.py
@@ -7,7 +7,7 @@
 
 from ..types import Center, LeftShift, Slope, TopShift
 from .abstract import Descaler
-from .complex import ComplexKernel, BorderHandling
+from .complex import BorderHandling, ComplexKernel
 
 __all__ = [
     'ZimgDescaler',
@@ -20,7 +20,7 @@ class ZimgDescaler(Descaler):
         @inject_self.cached
         @inject_kwargs_params
         def descale(  # type: ignore[override]
-            self, clip: vs.VideoNode, width: int, height: int, shift: tuple[TopShift, LeftShift] = (0, 0),
+            self, clip: vs.VideoNode, width: int | None, height: int | None, shift: tuple[TopShift, LeftShift] = (0, 0),
             *, blur: float = 1.0, border_handling: BorderHandling = BorderHandling.MIRROR, **kwargs: Any
         ) -> vs.VideoNode:
             ...
@@ -31,7 +31,7 @@ class ZimgComplexKernel(ComplexKernel, ZimgDescaler):  # type: ignore
         @inject_self.cached
         @inject_kwargs_params
         def descale(  # type: ignore[override]
-            self, clip: vs.VideoNode, width: int, height: int, shift: tuple[TopShift, LeftShift] = (0, 0),
+            self, clip: vs.VideoNode, width: int | None, height: int | None, shift: tuple[TopShift, LeftShift] = (0, 0),
             *, blur: float = 1.0, border_handling: BorderHandling, ignore_mask: vs.VideoNode | None = None,
             linear: bool = False, sigmoid: bool | tuple[Slope, Center] = False, **kwargs: Any
         ) -> vs.VideoNode:
diff --git a/vskernels/util.py b/vskernels/util.py
index 4fe0b79..1ce2d82 100644
--- a/vskernels/util.py
+++ b/vskernels/util.py
@@ -86,9 +86,11 @@ class NoScaleBase(Scaler):
     @inject_self.cached
     @inject_kwargs_params
     def scale(  # type: ignore
-        self, clip: vs.VideoNode, width: int, height: int, shift: tuple[TopShift, LeftShift] = (0, 0), **kwargs: Any
+        self, clip: vs.VideoNode, width: int | None = None, height: int | None = None,
+        shift: tuple[TopShift, LeftShift] = (0, 0), **kwargs: Any
     ) -> vs.VideoNode:
         try:
+            width, height = Scaler._wh_norm(clip, width, height)
             return super().scale(clip, clip.width, clip.height, shift, **kwargs)  # type: ignore
         except Exception:
             return clip