diff --git a/src/mono/mono/metadata/marshal.c b/src/mono/mono/metadata/marshal.c
index 1553ca1d1642c..f60de81c46bdd 100644
--- a/src/mono/mono/metadata/marshal.c
+++ b/src/mono/mono/metadata/marshal.c
@@ -4027,6 +4027,12 @@ emit_invoke_call (MonoMethodBuilder *mb, MonoMethod *method,
 	gboolean void_ret = FALSE;
 	gboolean string_ctor = method && method->string_ctor;
 
+	/* to make it work with our special string constructors */
+	if (!string_dummy) {
+		MONO_GC_REGISTER_ROOT_SINGLE (string_dummy, MONO_ROOT_SOURCE_MARSHAL, "dummy marshal string");
+		string_dummy = mono_string_new_wrapper ("dummy");
+	}
+
 	if (virtual_) {
 		g_assert (sig->hasthis);
 		g_assert (method->flags & METHOD_ATTRIBUTE_VIRTUAL);
@@ -4034,12 +4040,6 @@ emit_invoke_call (MonoMethodBuilder *mb, MonoMethod *method,
 
 	if (sig->hasthis) {
 		if (string_ctor) {
-			/* to make it work with our special string constructors */
-			if (!string_dummy) {
-				MONO_GC_REGISTER_ROOT_SINGLE (string_dummy, MONO_ROOT_SOURCE_MARSHAL, "dummy marshal string");
-				string_dummy = mono_string_new_wrapper ("dummy");
-			}
-
 			if (mono_gc_is_moving ()) {
 				mono_mb_emit_ptr (mb, &string_dummy);
 				mono_mb_emit_byte (mb, CEE_LDIND_REF);