diff --git a/elasticsearch-transport/elasticsearch-transport.gemspec b/elasticsearch-transport/elasticsearch-transport.gemspec
index 12e10a1172..a8c23780a9 100644
--- a/elasticsearch-transport/elasticsearch-transport.gemspec
+++ b/elasticsearch-transport/elasticsearch-transport.gemspec
@@ -44,6 +44,7 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = '>= 2.4'
 
+  s.add_dependency 'base64'
   s.add_dependency 'multi_json'
   s.add_dependency 'faraday', '>= 1', '< 3'