diff --git a/Notes.rst b/Notes.rst
index 7d27d8bcbd3e44c4e39b6432b8ff919707de2b8b..5189eab45bf1208e7d307d168e04781ba9bb119c 100644
--- a/Notes.rst
+++ b/Notes.rst
@@ -217,6 +217,11 @@
 		These seem to have cffi as a build-time dependency.
 		Cross-env gives the build pip env the host cffi .so so it fails.
 
+		Ah, but you can clobber this with::
+
+		  build-pip install cffi
+
+		And somehow this gets used instead.
 
           * Integrate a Python Tahoe-LAFS runtime with a GUI
 
diff --git a/crossenv/flake.nix b/crossenv/flake.nix
index fb083c9d51819eb1649be289bc39ce096445e2c4..f8b11f3c59db6cd9add5e693ff557607439ea35d 100644
--- a/crossenv/flake.nix
+++ b/crossenv/flake.nix
@@ -50,6 +50,15 @@
           # expose ffi header and library so we can build cffi, itself used by
           # various other Python packages
           cross-pkgs.libffi
+
+          # expose openssl header and library for python-cryptography build.
+          # It seems wrong that this is from native-pkgs, so maybe it is.
+          native-pkgs.openssl_1_1
+
+          # expose a native rust toolchain so we can build the rust-based
+          # Python extensions
+          native-pkgs.rustc
+          native-pkgs.cargo
         ];
 
         setupCrossEnv = ''
@@ -68,6 +77,11 @@
 
           # Activate the cross build environment for interactive use.
           . ./cross-env/bin/activate
+
+          # Now you can, eg,
+          #
+          # build-pip install a-build-dependency
+          # pip wheel somepackagetobuild
         '';
 
         shellHook = ''