diff --git a/README.md b/README.md
index 9751ec7..e38ad60 100644
--- a/README.md
+++ b/README.md
@@ -62,7 +62,7 @@ Constraints:
 | `null: false`    | `validates ... presence: true`                       |
 | `limit: 100`     | `validates ... length: { maximum: 100 }`             |
 | `unique: true`   | `validates ... uniqueness: true`                     |
-| `unique: true, case_sensitive: false` <br>(If [schema_plus_pg_indexes](https://github.com/SchemaPlus/schema_plus_pg_indexes) is also in use) | `validates ... uniqueness: { case_sensitive: false }` |
+| `unique: true, case_sensitive: false` <br>(Requires [schema_plus_pg_indexes](https://github.com/SchemaPlus/schema_plus_pg_indexes) for PostgreSQL) | `validates ... uniqueness: { case_sensitive: false }` |
 
 Data types:
 
diff --git a/lib/schema_validations/active_record/validations.rb b/lib/schema_validations/active_record/validations.rb
index d76d93d..d9be6d5 100644
--- a/lib/schema_validations/active_record/validations.rb
+++ b/lib/schema_validations/active_record/validations.rb
@@ -169,7 +169,7 @@ def add_uniqueness_validation(column) #:nodoc:
           options = {}
           options[:scope] = scope if scope.any?
           options[:allow_nil] = true
-          options[:case_sensitive] = false if has_case_insensitive_index?(column, scope)
+          options[:case_sensitive] = false if column_is_case_insensitive?(column) or has_case_insensitive_index?(column, scope)
           options[:if] = (proc do |record|
             if scope.all? { |scope_sym| record.public_send(:"#{scope_sym}?") }
               record.public_send(:"#{column.name}_changed?")
@@ -181,6 +181,10 @@ def add_uniqueness_validation(column) #:nodoc:
           validate_logged :validates_uniqueness_of, name, options
         end
 
+        def column_is_case_insensitive?(column)
+          column.respond_to?(:collation) && column.respond_to?(:case_sensitive?) && ! column.case_sensitive?
+        end
+
         def has_case_insensitive_index?(column, scope)
           indexed_columns = (scope + [column.name]).map(&:to_sym).sort
           index = column.indexes.select { |i| i.unique && i.columns.map(&:to_sym).sort == indexed_columns }.first