diff --git a/terraform/plan.go b/terraform/plan.go
index 739561f1f..05df1672f 100644
--- a/terraform/plan.go
+++ b/terraform/plan.go
@@ -14,6 +14,7 @@ import (
 func init() {
 	gob.Register(make([]interface{}, 0))
 	gob.Register(make([]map[string]interface{}, 0))
+	gob.Register(make(map[string]string))
 }
 
 // PlanOpts are the options used to generate an execution plan for