diff --git a/lib/mongo/collection.rb b/lib/mongo/collection.rb
index f9b9b1a668..12e53b76fb 100644
--- a/lib/mongo/collection.rb
+++ b/lib/mongo/collection.rb
@@ -518,8 +518,9 @@ def update(selector, document, opts={})
     # @option opts [Boolean] :unique (false) if true, this index will enforce a uniqueness constraint.
     # @option opts [Boolean] :background (false) indicate that the index should be built in the background. This
     #   feature is only available in MongoDB >= 1.3.2.
-    # @option opts [Boolean] :drop_dups (nil) If creating a unique index on a collection with pre-existing records,
-    #   this option will keep the first document the database indexes and drop all subsequent with duplicate values.
+    # @option opts [Boolean] :drop_dups (nil) (DEPRECATED) If creating a unique index on a collection with
+    #   pre-existing records, this option will keep the first document the database indexes and drop all subsequent
+    #   with duplicate values.
     # @option opts [Integer] :bucket_size (nil) For use with geoHaystack indexes. Number of documents to group
     #   together within a certain proximity to a given longitude and latitude.
     # @option opts [Integer] :min (nil) specify the minimum longitude and latitude for a geo index.
@@ -545,6 +546,10 @@ def update(selector, document, opts={})
     # @example A geospatial index with alternate longitude and latitude:
     #   @restaurants.create_index([['location', Mongo::GEO2D]], :min => 500, :max => 500)
     #
+    # @note The :drop_dups option is no longer supported by MongoDB starting with server version 2.7.5.
+    #   The option is silently ignored by the server and unique index builds using the option will
+    #   fail if a duplicate value is detected.
+    #
     # @return [String] the name of the index created.
     def create_index(spec, opts={})
       options              = opts.dup
@@ -572,6 +577,10 @@ def create_index(spec, opts={})
     #   Time t+10min : @posts.ensure_index(:subject => Mongo::ASCENDING) -- calls create_index and
     #     resets the 5 minute counter
     #
+    # @note The :drop_dups option is no longer supported by MongoDB starting with server version 2.7.5.
+    #   The option is silently ignored by the server and unique index builds using the option will
+    #   fail if a duplicate value is detected.
+    #
     # @return [String] the name of the index.
     def ensure_index(spec, opts={})
       now                  = Time.now.utc.to_i