diff --git a/nix/gem/Gemfile b/nix/gem/Gemfile
index af29a76..d9e52ce 100644
--- a/nix/gem/Gemfile
+++ b/nix/gem/Gemfile
@@ -19,7 +19,7 @@ gem "phrase", "2.20.0"
 gem "pry", "0.14.2"
 gem "psych", "5.1.1.1"
 gem "rake", "13.1.0"
-gem "rdoc", "6.6.0"
+gem "rdoc", "6.6.3.1"
 gem "reline", "0.4.1"
 gem "rspec", "3.12.0"
 gem "rspec-core", "3.12.2"
diff --git a/nix/gem/Gemfile.lock b/nix/gem/Gemfile.lock
index d4edc55..24303df 100644
--- a/nix/gem/Gemfile.lock
+++ b/nix/gem/Gemfile.lock
@@ -28,7 +28,7 @@ GEM
     psych (5.1.1.1)
       stringio
     rake (13.1.0)
-    rdoc (6.6.0)
+    rdoc (6.6.3.1)
       psych (>= 4.0.0)
     reline (0.4.1)
       io-console (~> 0.5)
@@ -74,7 +74,7 @@ DEPENDENCIES
   pry (= 0.14.2)
   psych (= 5.1.1.1)
   rake (= 13.1.0)
-  rdoc (= 6.6.0)
+  rdoc (= 6.6.3.1)
   reline (= 0.4.1)
   rspec (= 3.12.0)
   rspec-core (= 3.12.2)