The code

alias A B;
const int A = 1;

causes error

test.d(1): Error: alias test.B forward reference of A

This is caused by dmd not trusting it's forward reference capabilities and issuing the error without even trying:

Index: declaration.c
===================================================================
--- declaration.c	(revision 421)
+++ declaration.c	(working copy)
@@ -500,7 +500,7 @@
     //printf("alias is a symbol %s %s\n", s->kind(), s->toChars());
     type = NULL;
     VarDeclaration *v = s->isVarDeclaration();
-    if (v && v->linkage == LINKdefault)
+    if (0)
     {
 	error("forward reference of %s", v->toChars());
 	s = NULL;

(I thought this would be a duplicate, but the patch does not apply to any other bug i've tried).