diff --git a/dyaml/constructor.d b/dyaml/constructor.d
index fbaaa03..d766924 100644
--- a/dyaml/constructor.d
+++ b/dyaml/constructor.d
@@ -524,9 +524,9 @@ SysTime constructTimestamp(ref Node node)
 {
     string value = node.as!string;
 
-    immutable YMDRegexp = regex("^([0-9][0-9][0-9][0-9])-([0-9][0-9]?)-([0-9][0-9]?)");
-    immutable HMSRegexp = regex("^[Tt \t]+([0-9][0-9]?):([0-9][0-9]):([0-9][0-9])(\\.[0-9]*)?");
-    immutable TZRegexp  = regex("^[ \t]*Z|([-+][0-9][0-9]?)(:[0-9][0-9])?");
+    auto YMDRegexp = regex("^([0-9][0-9][0-9][0-9])-([0-9][0-9]?)-([0-9][0-9]?)");
+    auto HMSRegexp = regex("^[Tt \t]+([0-9][0-9]?):([0-9][0-9]):([0-9][0-9])(\\.[0-9]*)?");
+    auto TZRegexp  = regex("^[ \t]*Z|([-+][0-9][0-9]?)(:[0-9][0-9])?");
 
     try
     {