diff --git a/lib/kamal/configuration.rb b/lib/kamal/configuration.rb
index b60bb677..217c47c4 100644
--- a/lib/kamal/configuration.rb
+++ b/lib/kamal/configuration.rb
@@ -199,7 +199,7 @@ class Kamal::Configuration
 
   # Will raise KeyError if any secret ENVs are missing
   def ensure_env_available
-    roles.each(&:env_file)
+    roles.collect(&:env_file).each(&:to_s)
 
     true
   end