diff --git a/lib/github_changelog_generator/options.rb b/lib/github_changelog_generator/options.rb
index 20771ee..ac86740 100644
--- a/lib/github_changelog_generator/options.rb
+++ b/lib/github_changelog_generator/options.rb
@@ -2,6 +2,8 @@
 require 'delegate'
 module GitHubChangelogGenerator
   class Options < SimpleDelegator
+    UnsupportedOptionError = Class.new(ArgumentError)
+
     KNOWN_OPTIONS = [
       :add_issues_wo_labels,
       :add_pr_wo_labels,
@@ -56,9 +58,12 @@ module GitHubChangelogGenerator
 
     def initialize(values)
       super(values)
-      if unsupported_options.any?
-        raise ArgumentError, "Unsupported options #{unsupported_options}"
-      end
+      unsupported_options.any? && raise(UnsupportedOptionError, unsupported_options.inspect)
+    end
+
+    def []=(key, val)
+      supported_option?(key) || raise(UnsupportedOptionError, key.inspect)
+      values[key] = val
     end
 
     def to_hash
@@ -72,7 +77,15 @@ module GitHubChangelogGenerator
     end
 
     def unsupported_options
-      values.keys - (KNOWN_OPTIONS + THESE_ARE_DIFFERENT)
+      values.keys - supported_options
+    end
+
+    def supported_option?(key)
+      supported_options.include?(key)
+    end
+
+    def supported_options
+      KNOWN_OPTIONS + THESE_ARE_DIFFERENT
     end
   end
 end
diff --git a/spec/unit/options_spec.rb b/spec/unit/options_spec.rb
index c76b7ad..a3effc2 100644
--- a/spec/unit/options_spec.rb
+++ b/spec/unit/options_spec.rb
@@ -1,16 +1,42 @@
 # frozen_string_literal: true
-describe GitHubChangelogGenerator::Options do
-  it 'can be instantiated with defaults' do
-    expect(described_class.new(user: 'olle')[:user]).to eq('olle')
+RSpec.describe GitHubChangelogGenerator::Options do
+  describe "#initialize" do
+    context "with known options" do
+      it "instantiates successfully" do
+        expect(described_class.new(user: "olle")[:user]).to eq("olle")
+      end
+    end
+
+    context "with unknown options" do
+      it "raises an error" do
+        expect {
+          described_class.new(
+            git_remote: "origin",
+            strength: "super-strength",
+            wisdom: "deep"
+          )
+        }.to raise_error("[:strength, :wisdom]")
+      end
+    end
   end
 
-  it 'disallows unknown option names' do
-    expect {
-      described_class.new(
-        git_remote: 'origin',
-        strength: 'super-strength',
-        wisdom: 'deep'
-      )
-    }.to raise_error(ArgumentError, "Unsupported options [:strength, :wisdom]")
+  describe "#[]=(key, value)" do
+    let(:options) { described_class.new(git_remote: "origin") }
+
+    context "with known options" do
+      it "sets the option value" do
+        expect {
+          options[:git_remote] = "in the cloud"
+        }.to change { options[:git_remote] }.to "in the cloud"
+      end
+    end
+
+    context "with unknown options" do
+      it "raises an error" do
+        expect {
+          options[:charisma] = 8
+        }.to raise_error(":charisma")
+      end
+    end
   end
 end