diff --git a/lib/openapi3_parser/node_factory/paths.rb b/lib/openapi3_parser/node_factory/paths.rb
index 715e064..8d2074a 100644
--- a/lib/openapi3_parser/node_factory/paths.rb
+++ b/lib/openapi3_parser/node_factory/paths.rb
@@ -38,6 +38,7 @@ def build_node(data, node_context)
       def validate(validatable)
         paths = validatable.input.keys.grep_v(NodeFactory::EXTENSION_REGEX)
         validate_paths(validatable, paths)
+        validate_operation_ids(validatable)
       end
 
       def validate_paths(validatable, paths)
@@ -66,6 +67,31 @@ def conflicting_paths(paths)
 
         grouped_paths.select { |group| group.size > 1 }.flatten
       end
+
+      def validate_operation_ids(validatable)
+        operation_ids = []
+
+        validatable.input.each_value do |path_item|
+          next unless path_item.is_a?(Hash)
+
+          %w[get put post delete options head patch trace].each do |method|
+            operation = path_item[method]
+            next unless operation.is_a?(Hash)
+
+            operation_id = operation["operationId"]
+            operation_ids << operation_id if operation_id
+          end
+        end
+
+        counts = operation_ids.each_with_object(Hash.new(0)) { |id, hash| hash[id] += 1 }
+        dupes = counts.select { |_id, count| count > 1 }.keys
+
+        return if dupes.empty?
+
+        validatable.add_error(
+          "Duplicate operationId values: #{dupes.sort.join(', ')}"
+        )
+      end
     end
   end
 end
diff --git a/spec/lib/openapi3_parser/node_factory/openapi_spec.rb b/spec/lib/openapi3_parser/node_factory/openapi_spec.rb
index 0bddbe1..f2e6f76 100644
--- a/spec/lib/openapi3_parser/node_factory/openapi_spec.rb
+++ b/spec/lib/openapi3_parser/node_factory/openapi_spec.rb
@@ -59,6 +59,78 @@
     end
   end
 
+  describe "validating operationIds" do
+    it "is valid when operationIds are unique" do
+      factory_context = create_node_factory_context(
+        minimal_openapi_definition.merge(
+          "paths" => {
+            "/pets" => {
+              "get" => {
+                "operationId" => "listPets",
+                "responses" => { "200" => { "description" => "Success" } }
+              }
+            },
+            "/pets/{id}" => {
+              "get" => {
+                "operationId" => "getPet",
+                "responses" => { "200" => { "description" => "Success" } }
+              }
+            }
+          }
+        )
+      )
+      expect(described_class.new(factory_context)).to be_valid
+    end
+
+    it "is valid when some operations have no operationId" do
+      factory_context = create_node_factory_context(
+        minimal_openapi_definition.merge(
+          "paths" => {
+            "/pets" => {
+              "get" => {
+                "operationId" => "listPets",
+                "responses" => { "200" => { "description" => "Success" } }
+              }
+            },
+            "/pets/{id}" => {
+              "get" => {
+                "responses" => { "200" => { "description" => "Success" } }
+              }
+            }
+          }
+        )
+      )
+      expect(described_class.new(factory_context)).to be_valid
+    end
+
+    it "is invalid when operationIds are duplicated" do
+      factory_context = create_node_factory_context(
+        minimal_openapi_definition.merge(
+          "paths" => {
+            "/pets" => {
+              "get" => {
+                "operationId" => "getPets",
+                "responses" => { "200" => { "description" => "Success" } }
+              }
+            },
+            "/pets/{id}" => {
+              "get" => {
+                "operationId" => "getPets",
+                "responses" => { "200" => { "description" => "Success" } }
+              }
+            }
+          }
+        )
+      )
+
+      instance = described_class.new(factory_context)
+      expect(instance).not_to be_valid
+      expect(instance)
+        .to have_validation_error("#/paths")
+        .with_message("Duplicate operationId values: getPets")
+    end
+  end
+
   describe "default values for servers" do
     it "contains a basic root server when servers input is nil" do
       node = create_node(minimal_openapi_definition.merge({ "servers" => nil }))