diff --git a/src/include/cbmem.h b/src/include/cbmem.h
index 59f4e10..680284a 100644
--- a/src/include/cbmem.h
+++ b/src/include/cbmem.h
@@ -70,7 +70,8 @@
 
 /* Return the top address for dynamic cbmem. The address returned needs to
  * be consistent across romstage and ramstage, and it is required to be
- * below 4GiB.
+ * below 4GiB for 32bit coreboot builds. On 64bit coreboot builds there's no
+ * upper limit.
  * x86 boards or chipsets must return NULL before the cbmem backing store has
  * been initialized. */
 void *cbmem_top(void);