diff --git a/tools/yapp.pl b/tools/yapp.pl
index e8964ea..d93cf0c 100644
--- a/tools/yapp.pl
+++ b/tools/yapp.pl
@@ -89,7 +89,7 @@ sub DoPrepass
 
 	return "" if /^###/;
 	s/\s*###.*//;								# Strip comments
-	s/\${(\w+)}/&VarSubst($1, $skipFlag)/eg;	# Do variable substitutions
+	s/\$\{(\w+)}/&VarSubst($1, $skipFlag)/eg;	# Do variable substitutions
 	$_;
 }