diff --git a/terraform/main.tf b/terraform/main.tf
index 8e24bec..0657c6c 100644
--- a/terraform/main.tf
+++ b/terraform/main.tf
@@ -1,6 +1,9 @@
 locals {
   config = yamldecode(file(var.config))
 
+  allowed_top_level_keys  = ["repositories"]
+  allowed_repository_keys = ["name", "description", "homepage_url", "topics", "is_template", "template"]
+
   repository_defaults = {
     description  = null
     homepage_url = null
@@ -39,4 +42,15 @@ resource "github_repository" "this" {
       include_all_branches = try(template.value.include_all_branches, false)
     }
   }
+
+  lifecycle {
+    precondition {
+      condition     = length(setsubtract(keys(local.config), local.allowed_top_level_keys)) == 0
+      error_message = "Unknown top-level key(s) in ${var.config}: ${join(", ", setsubtract(keys(local.config), local.allowed_top_level_keys))}"
+    }
+    precondition {
+      condition     = length(setsubtract(keys(each.value), local.allowed_repository_keys)) == 0
+      error_message = "Unknown key(s) for repository ${each.key}: ${join(", ", setsubtract(keys(each.value), local.allowed_repository_keys))}"
+    }
+  }
 }