diff --git a/lib/dry/schema/dsl.rb b/lib/dry/schema/dsl.rb
index e3b453bb..b7067405 100644
--- a/lib/dry/schema/dsl.rb
+++ b/lib/dry/schema/dsl.rb
@@ -437,7 +437,7 @@ def parent_filter_schemas
       #
       # @api private
       def key_validator
-        KeyValidator.new(key_map: key_map + parent_key_map)
+        KeyValidator.new(key_map: key_map)
       end
 
       # Build a key coercer
diff --git a/spec/integration/schema/steps_spec.rb b/spec/integration/schema/steps_spec.rb
index b06f34a4..67f6f7b9 100644
--- a/spec/integration/schema/steps_spec.rb
+++ b/spec/integration/schema/steps_spec.rb
@@ -204,4 +204,24 @@
       }.to raise_error(ArgumentError, /oops/)
     end
   end
+
+  context "with an inherited params" do
+    describe "core step key maps" do
+      it "copies key map from the parent and includes new keys from child" do
+        parent = Dry::Schema.Params do
+          config.validate_keys = true
+
+          required(:name).filled(:string)
+        end
+
+        child = Dry::Schema.Params(parent: parent) do
+          required(:email).filled(:string)
+        end
+
+        %i[key_validator key_coercer].each do |step|
+          expect(child.steps[step].executor.key_map.map(&:name)).to eql(%w[name email])
+        end
+      end
+    end
+  end
 end
diff --git a/spec/integration/schema/unexpected_keys_spec.rb b/spec/integration/schema/unexpected_keys_spec.rb
index cde1d683..6771539a 100644
--- a/spec/integration/schema/unexpected_keys_spec.rb
+++ b/spec/integration/schema/unexpected_keys_spec.rb
@@ -150,4 +150,21 @@
       end
     end
   end
+
+  context "with an inherited params" do
+    it "copies key map from the parent and includes new keys from child" do
+      parent = Dry::Schema.Params do
+        config.validate_keys = true
+
+        required(:name).filled(:string)
+      end
+
+      child = Dry::Schema.Params(parent: parent) do
+        required(:email).filled(:string)
+      end
+
+      expect(child.(name: "Jane", email: "jane@doe.org", unexpected_key: "boo!").errors.to_h)
+        .to eql({unexpected_key: ["is not allowed"]})
+    end
+  end
 end