diff --git a/tools/build/options/WITH_BEARSSL b/tools/build/options/WITH_BEARSSL
--- a/tools/build/options/WITH_BEARSSL
+++ b/tools/build/options/WITH_BEARSSL
@@ -8,3 +8,16 @@
 signature verification and related operations
 for Verified Exec and
 .Xr loader 8 .
+.Pp
+Due to size constraints, one may need to set
+.Va LOADERSIZE
+larger than the
+default 500000, although often loader is under the 500k limit even with
+this option.
+Setting
+.Va LOADERSIZE
+larger than 500k may cause pxeldr to be too large to work.
+Careful testing of the loader in the target environment when built with a larger
+limit to establish safe limits is critical because different BIOS environments
+reserve differing amounts of the low 640k space, making a precise limit for
+everybody impossible.
diff --git a/tools/build/options/WITH_LOADER_VERIEXEC b/tools/build/options/WITH_LOADER_VERIEXEC
--- a/tools/build/options/WITH_LOADER_VERIEXEC
+++ b/tools/build/options/WITH_LOADER_VERIEXEC
@@ -4,3 +4,5 @@
 .Pp
 Depends on
 .Va WITH_BEARSSL .
+May require a larger
+.Va LOADERSIZE .