diff --git a/src/PmTcl/Commands.pm b/src/PmTcl/Commands.pm
index 9fb9b65..c7acc60 100644
--- a/src/PmTcl/Commands.pm
+++ b/src/PmTcl/Commands.pm
@@ -88,6 +88,9 @@ INIT {
 
 
 our sub eval(*@args) {
+    if +@args < 1 {
+        error('wrong # args: should be "eval arg ?arg ...?"');
+    }
     my $code := concat(|@args);
     our %EVALCACHE;
     my &sub := %EVALCACHE{$code};