diff --git a/plugins/script b/plugins/script
index c81aaa6..f725048 100755
--- a/plugins/script
+++ b/plugins/script
@@ -469,13 +469,16 @@ parse_word (struct tokenizer *self)
 	struct buffer buf = BUFFER_INITIALIZER;
 	char c;
 
-	// Here we accept almost anything that doesn't break the grammar...
+	// Here we accept almost anything that doesn't break the grammar
 	while (!strchr (" []\"", (c = *self->cursor++)) && (unsigned char) c > ' ')
 		buffer_append_c (&buf, c);
 	self->cursor--;
 
-	// ...so an empty word can only mean a bug within our caller.
-	assert (buf.len != 0);
+	if (!buf.len)
+	{
+		self->error = "invalid input";
+		return NULL;
+	}
 
 	struct item *item = new_word (buf.s, buf.len);
 	free (buf.s);