diff --git a/pkgs/applications/science/biology/ncbi-tools/default.nix b/pkgs/applications/science/biology/ncbi-tools/default.nix
index e47b1744da7..775e2ec3cc8 100644
--- a/pkgs/applications/science/biology/ncbi-tools/default.nix
+++ b/pkgs/applications/science/biology/ncbi-tools/default.nix
@@ -1,6 +1,11 @@
 {stdenv, fetchurl, cpio}:
 
-# Note: you may want the older C-libs at ftp://ftp.ncbi.nih.gov/toolbox/ncbi_tools++/2008/Mar_17_2008/NCBI_C_Toolkit/ncbi_c--Mar_17_2008.tar.gz
+# The NCBI package only builds on 32bits - on 64bits it breaks because
+# of position dependent code. Debian packagers have written replacement
+# make files(!). Either we use these, or negotiate a version which can
+# be pushed upstream to NCBI.
+#
+# Another note: you may want the older and deprecated C-libs at ftp://ftp.ncbi.nih.gov/toolbox/ncbi_tools++/2008/Mar_17_2008/NCBI_C_Toolkit/ncbi_c--Mar_17_2008.tar.gz
 
 stdenv.mkDerivation rec {
   name = "ncbi_tools";