diff --git a/sh/core/code.awk b/sh/core/code.awk
index a94ed93..1603cdd 100644
--- a/sh/core/code.awk
+++ b/sh/core/code.awk
@@ -249,6 +249,11 @@ if (action == "doc") {
 		unique[extract($0, target)] = ""
 	}
 
+# unknown
+} else {
+	print "unknown action: " action
+	exit 1
+
 # ← action
 }