diff --git a/lib/rubocop/rails/schema_loader/schema.rb b/lib/rubocop/rails/schema_loader/schema.rb
index cbb1882926..36d18b76ff 100644
--- a/lib/rubocop/rails/schema_loader/schema.rb
+++ b/lib/rubocop/rails/schema_loader/schema.rb
@@ -118,11 +118,11 @@ def analyze_keywords!(node)
 
       # Reprecent an index
       class Index
-        attr_reader :name, :columns, :unique
+        attr_reader :name, :columns, :expression, :unique
 
         def initialize(node)
           node.first_argument
-          @columns = build_columns(node)
+          @columns, @expression = build_columns_or_expr(node)
           @unique = nil
 
           analyze_keywords!(node)
@@ -130,8 +130,13 @@ def initialize(node)
 
         private
 
-        def build_columns(node)
-          node.first_argument.values.map(&:value)
+        def build_columns_or_expr(node)
+          arg = node.first_argument
+          if arg.array_type?
+            [arg.values.map(&:value), nil]
+          else
+            [[], arg.value]
+          end
         end
 
         def analyze_keywords!(node)
diff --git a/spec/rubocop/rails/schema_loader_spec.rb b/spec/rubocop/rails/schema_loader_spec.rb
index 81248508ff..29c0f55105 100644
--- a/spec/rubocop/rails/schema_loader_spec.rb
+++ b/spec/rubocop/rails/schema_loader_spec.rb
@@ -33,6 +33,7 @@
           create_table "articles", force: :cascade do |t|
             t.string "title", null: false
             t.bigint "user_id"
+            t.index 'lower(title)', name: 'index_title_lower_unique', unique: true
           end
         end
       RUBY
@@ -77,6 +78,13 @@
           expect(table.columns.size).to eq 2
           expect(table.columns.last.type).to eq :bigint
         end
+
+        it 'has an index in articles table' do
+          table = loaded_schema.table_by(name: 'articles')
+          expect(table.indices.size).to eq 1
+          expect(table.indices.first.name).to eq 'index_title_lower_unique'
+          expect(table.indices.first.unique).to be true
+        end
       end
 
       context 'when the current directory is Rails.root' do