diff --git a/lib/datadog/tracing/contrib/rack/middlewares.rb b/lib/datadog/tracing/contrib/rack/middlewares.rb
index 3c4f43d3f61..fc2662c95ca 100644
--- a/lib/datadog/tracing/contrib/rack/middlewares.rb
+++ b/lib/datadog/tracing/contrib/rack/middlewares.rb
@@ -147,7 +147,7 @@ def set_request_tags!(trace, request_span, env, status, headers, response, origi
               #
               # To account for the unaccounted nested rack requests of /rack/hello/world,
               # we use 'PATH_INFO knowing that rack cannot have named parameters
-              if last_script_name == '' && env['SCRIPT_NAME'] != ''
+              if last_script_name == '' && env['SCRIPT_NAME'] && env['SCRIPT_NAME'] != ''
                 last_script_name = last_route
                 last_route = env['PATH_INFO']
               end