diff --git a/command/test-fixtures/hcl2_upgrade/complete-variables-with-template-engine/expected.pkr.hcl b/command/test-fixtures/hcl2_upgrade/complete-variables-with-template-engine/expected.pkr.hcl
index 1116310d6..1bf776b6f 100644
--- a/command/test-fixtures/hcl2_upgrade/complete-variables-with-template-engine/expected.pkr.hcl
+++ b/command/test-fixtures/hcl2_upgrade/complete-variables-with-template-engine/expected.pkr.hcl
@@ -5,6 +5,7 @@ variable "env_test" {
 }
 
 locals { timestamp = regex_replace(timestamp(), "[- TZ:]", "") }
+# The "legacy_isotime" function has been provided for backwards compatability, but we recommend switching to the timestamp and formatdate functions.
 
 # 5 errors occurred upgrading the following block:
 # unhandled "lower" call:
@@ -33,7 +34,7 @@ locals { timestamp = regex_replace(timestamp(), "[- TZ:]", "") }
 # Visit https://www.packer.io/docs/templates/hcl_templates/functions/string/upper for more infos.
 locals {
   build_timestamp = "${local.timestamp}"
-  iso_datetime    = "${local.timestamp}"
+  iso_datetime    = "${legacy_isotime("2006-01-02T15:04:05Z07:00")}"
   lower           = "{{ lower `HELLO` }}"
   pwd             = "${path.cwd}"
   replace         = "{{ replace `b` `c` `ababa` 2 }}"
diff --git a/command/test-fixtures/hcl2_upgrade/complete/expected.pkr.hcl b/command/test-fixtures/hcl2_upgrade/complete/expected.pkr.hcl
index 67e127138..3f1a46150 100644
--- a/command/test-fixtures/hcl2_upgrade/complete/expected.pkr.hcl
+++ b/command/test-fixtures/hcl2_upgrade/complete/expected.pkr.hcl
@@ -198,7 +198,7 @@ build {
   # Please manually upgrade to use custom validation rules, `replace(string, substring, replacement)` or `regex_replace(string, substring, replacement)`
   # Visit https://packer.io/docs/templates/hcl_templates/variables#custom-validation-rules , https://www.packer.io/docs/templates/hcl_templates/functions/string/replace or https://www.packer.io/docs/templates/hcl_templates/functions/string/regex_replace for more infos.
   provisioner "shell" {
-    inline = ["echo mybuild-{{ clean_resource_name `${local.timestamp}` }}"]
+    inline = ["echo mybuild-{{ clean_resource_name `${timestamp()}` }}"]
   }
 
 
diff --git a/command/test-fixtures/hcl2_upgrade/without-annotations/expected.pkr.hcl b/command/test-fixtures/hcl2_upgrade/without-annotations/expected.pkr.hcl
index 93c51bdc4..e332c21e0 100644
--- a/command/test-fixtures/hcl2_upgrade/without-annotations/expected.pkr.hcl
+++ b/command/test-fixtures/hcl2_upgrade/without-annotations/expected.pkr.hcl
@@ -151,7 +151,7 @@ build {
   # Please manually upgrade to use custom validation rules, `replace(string, substring, replacement)` or `regex_replace(string, substring, replacement)`
   # Visit https://packer.io/docs/templates/hcl_templates/variables#custom-validation-rules , https://www.packer.io/docs/templates/hcl_templates/functions/string/replace or https://www.packer.io/docs/templates/hcl_templates/functions/string/regex_replace for more infos.
   provisioner "shell" {
-    inline = ["echo mybuild-{{ clean_resource_name `${local.timestamp}` }}"]
+    inline = ["echo mybuild-{{ clean_resource_name `${timestamp()}` }}"]
   }