diff --git a/aws_project_costs/project-cost-schema.json b/aws_project_costs/project-cost-schema.json
index bfb466f..ed0bfba 100644
--- a/aws_project_costs/project-cost-schema.json
+++ b/aws_project_costs/project-cost-schema.json
@@ -5,7 +5,7 @@
   "type": "object",
   "properties": {
     "proj-tag-names": {
-      "description": "A mapping of AWS project tags to the canonical project name",
+      "description": "A mapping of AWS project tags to the canonical project name. Optionally use '*' to map unknown tags to a defined project name",
       "type": "object",
       "additionalProperties": {
         "type": "string",
diff --git a/aws_project_costs/project_costs.py b/aws_project_costs/project_costs.py
index 0f255a4..9d96752 100644
--- a/aws_project_costs/project_costs.py
+++ b/aws_project_costs/project_costs.py
@@ -82,9 +82,12 @@ def _shared_account(
 
         project_tag = costs_tag[5:]
         if project_tagname and project_tag and (project_tag not in shared_tag_values):
-            if project_tag not in proj_tag_names_map:
+            if project_tag in proj_tag_names_map:
+                project_name = proj_tag_names_map[project_tag]
+            elif "*" in proj_tag_names_map:
+                project_name = proj_tag_names_map["*"]
+            else:
                 raise ValueError(f"{project_tag} is not in proj-tag-names")
-            project_name = proj_tag_names_map[project_tag]
             rows.append(
                 (
                     start.date().isoformat(),