diff --git a/ets2panda/util/diagnostic/fatal.yaml b/ets2panda/util/diagnostic/fatal.yaml
index 5cd41417335a7e0d709bd20cf07461d914a844cd..2994683e1197f857ae081c319eeefcb55ce764d0 100644
--- a/ets2panda/util/diagnostic/fatal.yaml
+++ b/ets2panda/util/diagnostic/fatal.yaml
@@ -50,7 +50,7 @@ fatal:
 
 - name: UNKNOWN_EXT
   id: 10
-  message: "Unknown extension of sourcefile, set the '--extension' option or change the file extension (available options: js, ts, as, ets)"
+  message: "Unknown extension of sourcefile, set the '--extension' option or change the file extension (available options: ets)"
 
 - name: JS_UNSUPPORTED
   id: 11
diff --git a/ets2panda/util/options.cpp b/ets2panda/util/options.cpp
index 82dc27f031d73a9ca3cd4ab534eeddcc69b0096a..0569ff3a666456d78690f38d6637973afd1c81d8 100644
--- a/ets2panda/util/options.cpp
+++ b/ets2panda/util/options.cpp
@@ -371,6 +371,11 @@ bool Options::DetermineExtension()
             }
             return true;
         }
+        case ScriptExtension::AS:
+        case ScriptExtension::TS: {
+            diagnosticEngine_.LogDiagnostic(diagnostic::UNKNOWN_EXT, util::DiagnosticMessageParams {});
+            return false;
+        }
         default:
             return true;
     }
diff --git a/ets2panda/util/options.yaml b/ets2panda/util/options.yaml
index 7b57d1927b23350f838198eb625cc14bcfbc8b6e..af4b0e3bb2f6c06e54d4452c63ff5773d58f4501 100644
--- a/ets2panda/util/options.yaml
+++ b/ets2panda/util/options.yaml
@@ -37,7 +37,8 @@ options:
   - ts
   - as
   - ets
-  possible_values: *ScriptExtension
+  possible_values:
+    - ets
 
 - name: module
   type: bool