diff --git a/Library/Homebrew/cask/dsl/depends_on.rb b/Library/Homebrew/cask/dsl/depends_on.rb
index b8f701ab11..e8beba968d 100644
--- a/Library/Homebrew/cask/dsl/depends_on.rb
+++ b/Library/Homebrew/cask/dsl/depends_on.rb
@@ -63,8 +63,8 @@ module Cask
           else
             MacOSRequirement.new([args.first], comparator: "==")
           end
-        rescue MacOSVersionError
-          raise "invalid 'depends_on macos' value: #{args.first.inspect}"
+        rescue MacOSVersionError => e
+          raise "invalid 'depends_on macos' value: #{e}"
         end
       end
 
diff --git a/Library/Homebrew/os/mac/sdk.rb b/Library/Homebrew/os/mac/sdk.rb
index 54bed4fabb..ff30e3eaa2 100644
--- a/Library/Homebrew/os/mac/sdk.rb
+++ b/Library/Homebrew/os/mac/sdk.rb
@@ -11,7 +11,7 @@ module OS
       attr_reader :version, :path, :source
 
       def initialize(version, path, source)
-        @version = OS::Mac::Version.new version
+        @version = version
         @path = Pathname.new(path)
         @source = source
       end
@@ -33,7 +33,7 @@ module OS
       def latest_sdk
         return if sdk_paths.empty?
 
-        v, path = sdk_paths.max { |a, b| OS::Mac::Version.new(a[0]) <=> OS::Mac::Version.new(b[0]) }
+        v, path = sdk_paths.max(&:first)
         SDK.new v, path, source
       end
 
@@ -77,7 +77,7 @@ module OS
 
             Dir[File.join(sdk_prefix, "MacOSX*.sdk")].each do |sdk_path|
               version = sdk_path[/MacOSX(\d+\.\d+)u?\.sdk$/, 1]
-              paths[version] = sdk_path unless version.nil?
+              paths[OS::Mac::Version.new(version)] = sdk_path unless version.nil?
             end
 
             paths
diff --git a/Library/Homebrew/os/mac/version.rb b/Library/Homebrew/os/mac/version.rb
index 1c47f9ee88..3aadfb95d7 100644
--- a/Library/Homebrew/os/mac/version.rb
+++ b/Library/Homebrew/os/mac/version.rb
@@ -24,15 +24,18 @@ module OS
         new(str)
       end
 
-      def initialize(*args)
-        super
+      def initialize(value)
+        super(value)
+
+        raise MacOSVersionError, value unless value.match?(/\A1\d+(?:\.\d+){0,2}\Z/)
+
         @comparison_cache = {}
       end
 
       def <=>(other)
         @comparison_cache.fetch(other) do
           v = SYMBOLS.fetch(other) { other.to_s }
-          @comparison_cache[other] = super(Version.new(v))
+          @comparison_cache[other] = super(::Version.new(v))
         end
       end
 
diff --git a/Library/Homebrew/test/os/mac/software_spec_spec.rb b/Library/Homebrew/test/os/mac/software_spec_spec.rb
index 1d6501ed91..af94ef6f52 100644
--- a/Library/Homebrew/test/os/mac/software_spec_spec.rb
+++ b/Library/Homebrew/test/os/mac/software_spec_spec.rb
@@ -7,10 +7,8 @@ describe SoftwareSpec do
 
   describe "#uses_from_macos" do
     before do
-      sierra_os_version = OS::Mac::Version.from_symbol(:sierra)
-
       allow(OS).to receive(:mac?).and_return(true)
-      allow(OS::Mac).to receive(:version).and_return(OS::Mac::Version.new(sierra_os_version))
+      allow(OS::Mac).to receive(:version).and_return(OS::Mac::Version.from_symbol(:sierra))
     end
 
     it "adds a macOS dependency if the OS version meets requirements" do
diff --git a/Library/Homebrew/test/os/mac/version_spec.rb b/Library/Homebrew/test/os/mac/version_spec.rb
index 40c51974cb..3f332ed5aa 100644
--- a/Library/Homebrew/test/os/mac/version_spec.rb
+++ b/Library/Homebrew/test/os/mac/version_spec.rb
@@ -4,41 +4,49 @@ require "version"
 require "os/mac/version"
 
 describe OS::Mac::Version do
-  subject { described_class.new("10.14") }
+  subject(:version) { described_class.new("10.14") }
 
   specify "comparison with Symbol" do
-    expect(subject).to be > :high_sierra
-    expect(subject).to be == :mojave
-    expect(subject).to be === :mojave # rubocop:disable Style/CaseEquality
-    expect(subject).to be < :catalina
+    expect(version).to be > :high_sierra
+    expect(version).to be == :mojave
+    expect(version).to be === :mojave # rubocop:disable Style/CaseEquality
+    expect(version).to be < :catalina
   end
 
   specify "comparison with Fixnum" do
-    expect(subject).to be > 10
-    expect(subject).to be < 11
+    expect(version).to be > 10
+    expect(version).to be < 11
   end
 
   specify "comparison with Float" do
-    expect(subject).to be > 10.13
-    expect(subject).to be < 10.15
+    expect(version).to be > 10.13
+    expect(version).to be < 10.15
   end
 
   specify "comparison with String" do
-    expect(subject).to be > "10.3"
-    expect(subject).to be == "10.14"
-    expect(subject).to be === "10.14" # rubocop:disable Style/CaseEquality
-    expect(subject).to be < "10.15"
+    expect(version).to be > "10.3"
+    expect(version).to be == "10.14"
+    expect(version).to be === "10.14" # rubocop:disable Style/CaseEquality
+    expect(version).to be < "10.15"
   end
 
   specify "comparison with Version" do
-    expect(subject).to be > Version.create("10.3")
-    expect(subject).to be == Version.create("10.14")
-    expect(subject).to be === Version.create("10.14") # rubocop:disable Style/CaseEquality
-    expect(subject).to be < Version.create("10.15")
+    expect(version).to be > Version.create("10.3")
+    expect(version).to be == Version.create("10.14")
+    expect(version).to be === Version.create("10.14") # rubocop:disable Style/CaseEquality
+    expect(version).to be < Version.create("10.15")
+  end
+
+  describe "#new" do
+    it "raises an error if the version is not a valid macOS version" do
+      expect {
+        described_class.new("1.2")
+      }.to raise_error(MacOSVersionError, 'unknown or unsupported macOS version: "1.2"')
+    end
   end
 
   specify "#from_symbol" do
-    expect(described_class.from_symbol(:mojave)).to eq(subject)
+    expect(described_class.from_symbol(:mojave)).to eq(version)
     expect { described_class.from_symbol(:foo) }
       .to raise_error(MacOSVersionError, "unknown or unsupported macOS version: :foo")
   end