diff --git a/terraform/resource_address.go b/terraform/resource_address.go
index f7b3519789..156ecf5c0e 100644
--- a/terraform/resource_address.go
+++ b/terraform/resource_address.go
@@ -362,7 +362,7 @@ func NewLegacyResourceInstanceAddress(addr addrs.AbsResourceInstance) *ResourceA
 	ret.Path = path
 
 	if addr.Resource.Key == addrs.NoKey {
-		ret.Index = 0
+		ret.Index = -1
 	} else if ik, ok := addr.Resource.Key.(addrs.IntKey); ok {
 		ret.Index = int(ik)
 	} else {