diff --git a/meat.nu b/meat.nu
index 51dc8e3..a7373e9 100644
--- a/meat.nu
+++ b/meat.nu
@@ -43,7 +43,19 @@ def nix-conf-attr []: nothing -> string {
 }
 
 def nix-build-nom [out: string, source: string, attr: string, extras: list<string> = []] {
-  ^nix-build --log-format internal-json -v --out-link $out $source -A $attr ...$extras out+err>| ^$env.MONITOR --json
+  if ($env.MONITOR? | is-empty) {
+    ^nix-build --out-link $out $source -A $attr ...$extras
+  } else {
+    ^nix-build --log-format internal-json -v --out-link $out $source -A $attr ...$extras out+err>| ^$env.MONITOR --json
+  }
+}
+
+def differ-step [build: string] {
+  if ($env.DIFFER? | is-empty) {
+    meat-print "  (no DIFFER set; skipping diff)"
+  } else {
+    ^$env.DIFFER /nix/var/nix/profiles/system $build
+  }
 }
 
 def activate [build_path: string] {
@@ -54,7 +66,7 @@ def do-build [extras: list<string> = []] {
   let tmpdir = ^mktemp -d -t "meat-build.XXXXXX" | str trim
   let build = $"($tmpdir)/build"
   nix-build-nom $build $"($env.MEATS)/entry.nix" (system-attr) $extras
-  ^$env.DIFFER /nix/var/nix/profiles/system $build
+  differ-step $build
   activate $build
   try { rm $build }
 }
diff --git a/nix/default.nix b/nix/default.nix
index 10216e6..4b5d5ff 100644
--- a/nix/default.nix
+++ b/nix/default.nix
@@ -25,8 +25,8 @@ stdenvNoCC.mkDerivation {
     mkdir -p $out/bin
     makeBinaryWrapper ${nushell}/bin/nu $out/bin/meat \
       --add-flags "$out/share/meat/meat.nu" \
-      --set DIFFER ${lib.makeBinPath [ differ ]} \
-      --set MONITOR ${lib.makeBinPath [ monitor ]}
+      --set DIFFER ${lib.getExe differ} \
+      --set MONITOR ${lib.getExe monitor}
     runHook postInstall
   '';
 }