diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index f39c7c9..9496948 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -35,7 +35,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: ["3.3", "3.4", "4.0"]
+        ruby: ["3.4", "4.0"]
     services:
       postgres:
         image: postgres:latest
diff --git a/.rubocop.yml b/.rubocop.yml
index d146353..5928ff8 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -9,7 +9,7 @@ plugins:
 AllCops:
   NewCops: enable
   TargetRailsVersion: 7.2
-  TargetRubyVersion: 3.3
+  TargetRubyVersion: 3.4
   Exclude:
     - 'spec/internal/config/**/*'
     - 'spec/internal/db/**/*'
diff --git a/dynamic_image.gemspec b/dynamic_image.gemspec
index 92b8769..586c0cf 100644
--- a/dynamic_image.gemspec
+++ b/dynamic_image.gemspec
@@ -24,7 +24,7 @@ Gem::Specification.new do |s|
     "README.md"
   ]
 
-  s.required_ruby_version = ">= 3.3.0"
+  s.required_ruby_version = ">= 3.4.0"
 
   s.add_dependency "dis", "~> 2.1"
   s.add_dependency "rails", "> 7.0"
diff --git a/lib/dynamic_image/breakpoints.rb b/lib/dynamic_image/breakpoints.rb
index e5539a4..e8f6361 100644
--- a/lib/dynamic_image/breakpoints.rb
+++ b/lib/dynamic_image/breakpoints.rb
@@ -61,15 +61,15 @@ def widths(available)
     private
 
     def fixed(available)
-      widths = spec.map(&:to_i).select { _1 <= available }.uniq.sort
+      widths = spec.map(&:to_i).select { it <= available }.uniq.sort
       widths.any? ? widths : [available]
     end
 
     def stepped(available)
       top = [available, spec.end || available].min
-      rest = Enumerator.produce(top / step) { _1 / step }
-                       .take_while { _1 >= spec.begin }
-                       .map { snap(_1) }
+      rest = Enumerator.produce(top / step) { it / step }
+                       .take_while { it >= spec.begin }
+                       .map { snap(it) }
 
       [top, *rest].reverse.uniq
     end
diff --git a/lib/dynamic_image/errors.rb b/lib/dynamic_image/errors.rb
index b8bae16..7b386bf 100644
--- a/lib/dynamic_image/errors.rb
+++ b/lib/dynamic_image/errors.rb
@@ -28,9 +28,10 @@ class InvalidHeader < DynamicImage::Errors::Error; end
     # @see DynamicImage::DigestVerifier#verify
     class InvalidSignature < DynamicImage::Errors::Error; end
 
-    # Raised when a size can't be rendered. Either cropping was requested without both dimensions, as in
+    # Raised when a size can't be rendered. Cropping was requested without both dimensions, as in
     # <tt>size: "400x", crop: true</tt> — there is no way to crop to an exact size when one of them is unknown — or
-    # the size works out to less than a pixel, as <tt>"0x0"</tt> does, or <tt>"1x1"</tt> against a very wide image.
+    # the size is zero on both axes, as <tt>"0x0"</tt> is, and constrains nothing, or the size works out to less
+    # than a pixel, as <tt>"1x1"</tt> does against a very wide image.
     #
     # @see DynamicImage::ImageSizing#fit
     # @see DynamicImage::Model::Transformations#resize
diff --git a/lib/dynamic_image/image_sizing.rb b/lib/dynamic_image/image_sizing.rb
index 48b4a19..f4cbfdb 100644
--- a/lib/dynamic_image/image_sizing.rb
+++ b/lib/dynamic_image/image_sizing.rb
@@ -27,6 +27,7 @@ def initialize(record, options = {})
     #
     # @param ratio_vector [Vector2d] the aspect ratio to crop to
     # @return [Array(Vector2d, Vector2d)] the crop size and crop start
+    # @raise [DynamicImage::Errors::InvalidSizeOptions] if the vector is zero on both axes
     #
     # @example
     #   image = Image.find(params[:id]) # 320x200 image
@@ -35,6 +36,8 @@ def initialize(record, options = {})
     #   sizing.crop_geometry(Vector2d(100, 100))
     #   # => [Vector2d(200, 200), Vector2d(60, 0)]
     def crop_geometry(ratio_vector)
+      require_nonzero!(ratio_vector)
+
       # Maximize the crop area to fit the image size
       crop_size = ratio_vector.fit(size).round
 
@@ -66,7 +69,7 @@ def available_width(ratio = nil)
       ratio = DynamicImage::Ratio.parse(ratio)
       return size.x.floor unless ratio
 
-      crop_geometry(vector(ratio, 1)).first.x.floor
+      crop_geometry(Vector2d.new(ratio, 1)).first.x.floor
     end
 
     # Adjusts +fit_size+ to fit the image dimensions. Any dimension set to zero will be ignored.
@@ -80,7 +83,7 @@ def available_width(ratio = nil)
     #   be scaled up.
     # @return [Vector2d] the resulting size
     # @raise [DynamicImage::Errors::InvalidSizeOptions] if <tt>crop: true</tt> is given and either dimension is zero,
-    #   or if the result is less than a pixel in either dimension
+    #   if the size is zero on both axes, or if the result is less than a pixel in either dimension
     #
     # @example
     #   image = Image.find(params[:id]) # 320x200 image
@@ -100,6 +103,7 @@ def available_width(ratio = nil)
     def fit(fit_size, options = {})
       fit_size = parse_vector(fit_size)
       require_dimensions!(fit_size) if options[:crop]
+      require_nonzero!(fit_size)
       fit_size = size.fit(fit_size) unless options[:crop]
       fit_size = contain(fit_size)  unless options[:upscale]
       fit_size = snap(fit_size)
@@ -163,8 +167,16 @@ def require_dimensions!(vector)
             "both dimensions are required when cropping"
     end
 
+    # Rejects a vector that is zero on both axes. A single zero axis means the axis is unconstrained, but a vector
+    # that is zero throughout constrains nothing and describes no image.
+    def require_nonzero!(vector)
+      return unless vector.x.zero? && vector.y.zero?
+
+      raise DynamicImage::Errors::InvalidSizeOptions, "#{vector} has no size"
+    end
+
     # Rejects sizes that don't round to at least one pixel in each dimension, since there is no image to render at
-    # that point. A NaN, which is what an empty size fits to, fails this too.
+    # that point.
     def require_pixels!(vector)
       return if vector.x >= 1 && vector.y >= 1
 
@@ -173,7 +185,7 @@ def require_pixels!(vector)
     end
 
     def shift_vector(vect)
-      vector(
+      Vector2d.new(
         vect.x.negative? ? vect.x.abs : 0,
         vect.y.negative? ? vect.y.abs : 0
       )
@@ -183,7 +195,7 @@ def shift_vector(vect)
     # point, so an axis that should land exactly on a pixel can come out a few ulps below it, and callers flooring
     # the result would lose that pixel.
     def snap(scaled)
-      vector(snap_axis(scaled.x), snap_axis(scaled.y))
+      Vector2d.new(snap_axis(scaled.x), snap_axis(scaled.y))
     end
 
     def snap_axis(value)
@@ -201,9 +213,5 @@ def str_to_vector(str)
     def uncropped?
       @uncropped
     end
-
-    def vector(width, height)
-      Vector2d.new(width, height)
-    end
   end
 end
diff --git a/lib/dynamic_image/model/transformations.rb b/lib/dynamic_image/model/transformations.rb
index 4f8dafe..fcc0ad1 100644
--- a/lib/dynamic_image/model/transformations.rb
+++ b/lib/dynamic_image/model/transformations.rb
@@ -17,7 +17,8 @@ module Transformations
       # @param max_size [Vector2d, String] the size to fit within, either a vector or a <tt>"{width}x{height}"</tt>
       #   string. Either dimension may be omitted to scale by the other alone.
       # @return [self]
-      # @raise [DynamicImage::Errors::InvalidSizeOptions] if the result is less than a pixel in either dimension
+      # @raise [DynamicImage::Errors::InvalidSizeOptions] if the size is zero on both axes, or if the result is less
+      #   than a pixel in either dimension
       # @raise [DynamicImage::Errors::InvalidImage] if the stored data can't be processed
       def resize(max_size)
         transform_image do |image|
@@ -55,9 +56,14 @@ def rotate(degrees = 90)
 
       private
 
-      # Scales +max_size+ against the image, rejecting a result smaller than a pixel in either dimension, as
-      # {DynamicImage::ImageSizing#fit} does for the sizes rendered on request.
+      # Scales +max_size+ against the image, rejecting a size that is zero on both axes and a result smaller than a
+      # pixel in either dimension, as {DynamicImage::ImageSizing#fit} does for the sizes rendered on request.
       def fit_size(max_size)
+        max_size = Vector2d.parse(max_size)
+        if max_size.x.zero? && max_size.y.zero?
+          raise DynamicImage::Errors::InvalidSizeOptions, "#{max_size} has no size"
+        end
+
         new_size = real_size.fit(max_size)
         return new_size if new_size.x >= 1 && new_size.y >= 1
 
diff --git a/spec/dynamic_image/image_sizing_spec.rb b/spec/dynamic_image/image_sizing_spec.rb
index 12fc265..11d37f6 100644
--- a/spec/dynamic_image/image_sizing_spec.rb
+++ b/spec/dynamic_image/image_sizing_spec.rb
@@ -58,6 +58,14 @@ def v(width, height)
 
       it { is_expected.to eq([v(200, 200), v(120, 0)]) }
     end
+
+    context "with both dimensions zero" do
+      it "raises an error" do
+        expect { crop_geometry(0, 0) }.to(
+          raise_error(DynamicImage::Errors::InvalidSizeOptions)
+        )
+      end
+    end
   end
 
   describe "#crop_geometry (cropped image)" do
diff --git a/spec/dynamic_image/model/transformations_spec.rb b/spec/dynamic_image/model/transformations_spec.rb
index 23ecc22..257cd76 100644
--- a/spec/dynamic_image/model/transformations_spec.rb
+++ b/spec/dynamic_image/model/transformations_spec.rb
@@ -79,6 +79,16 @@
     end
 
     context "when the size is smaller than a pixel" do
+      subject(:resized) { image.resize("1x1") }
+
+      it "raises an error" do
+        expect { resized }.to(
+          raise_error(DynamicImage::Errors::InvalidSizeOptions)
+        )
+      end
+    end
+
+    context "with both dimensions zero" do
       subject(:resized) { image.resize("0x0") }
 
       it "raises an error" do