diff --git a/lib/image-builder/makeFAT32.nix b/lib/image-builder/makeFAT32.nix
index 4687cd46..4081ca3c 100644
--- a/lib/image-builder/makeFAT32.nix
+++ b/lib/image-builder/makeFAT32.nix
@@ -1,4 +1,4 @@
-{ makeFilesystem, dosfstools, mtools, libfaketime }:
+{ makeFilesystem, dosfstools, mtools, libfaketime, size }:
 
 /*  */ let scope = { "fileSystem.makeFAT32" =
 
@@ -7,6 +7,8 @@ makeFilesystem (args // {
   # FAT32 can be used for ESP. Let's make this obvious.
   filesystemType = if args ? filesystemType then args.filesystemType else "FAT32";
 
+  minimumSize = size.KiB 500;
+
   nativeBuildInputs = [
     libfaketime
     dosfstools
diff --git a/lib/image-builder/makeFilesystem.nix b/lib/image-builder/makeFilesystem.nix
index c781f0fc..5f296286 100644
--- a/lib/image-builder/makeFilesystem.nix
+++ b/lib/image-builder/makeFilesystem.nix
@@ -1,10 +1,9 @@
-{ stdenvNoCC, lib, writeText, size }:
+{ stdenvNoCC, lib, writeText }:
 
 /*  */ let scope = { "fileSystem.makeFilesystem" =
 
 let
   inherit (lib) optionals optionalString assertMsg;
-  minimumSize = toString (size.KiB 500);
 in
 
 {
@@ -58,9 +57,9 @@ stdenvNoCC.mkDerivation (args // rec {
     size=$(cd files; du -sb --apparent-size . | tr -cd '[:digit:]')
     ''}
 
-    if (( size < ${minimumSize} )); then
-      size=${minimumSize}
-      echo "WARNING: partition was too small, size increased to ${minimumSize} bytes."
+    if (( size < minimumSize )); then
+      size=$minimumSize
+      echo "WARNING: partition was too small, size increased to $minimumSize bytes."
     fi
 
     echo