diff --git a/devices/gl-ar750/default.nix b/devices/gl-ar750/default.nix
index 9418241..2d1ab23 100644
--- a/devices/gl-ar750/default.nix
+++ b/devices/gl-ar750/default.nix
@@ -106,9 +106,9 @@
         loadAddress = lim.parseInt "0x80060000";
         entryPoint = lim.parseInt "0x80060000";
         flash = {
-          address = "0x9F060000";
-          size ="0xfa0000";
-          eraseBlockSize = "65536";
+          address = lim.parseInt "0x9F060000";
+          size = lim.parseInt "0xfa0000";
+          eraseBlockSize = 65536;
         };
         rootDevice = "/dev/mtdblock5";
         dts = {
diff --git a/devices/gl-mt300a/default.nix b/devices/gl-mt300a/default.nix
index 28ca20e..3fa9c38 100644
--- a/devices/gl-mt300a/default.nix
+++ b/devices/gl-mt300a/default.nix
@@ -69,9 +69,9 @@
         # 0x000000260000-0x000000f80000 : "rootfs"
 
         flash = {
-          address = "0xbc050000";
-          size ="0xf80000";
-          eraseBlockSize = "65536";
+          address = lim.parseInt "0xbc050000";
+          size = lim.parseInt "0xf80000";
+          eraseBlockSize = 65536;
         };
         rootDevice = "/dev/mtdblock5";
 
diff --git a/devices/gl-mt300n-v2/default.nix b/devices/gl-mt300n-v2/default.nix
index e3d1774..c1dea49 100644
--- a/devices/gl-mt300n-v2/default.nix
+++ b/devices/gl-mt300n-v2/default.nix
@@ -66,9 +66,9 @@
         entryPoint = lim.parseInt "0x80000000";
 
         flash = {
-          address = "0xbc050000";
-          size = "0xfb0000";
-          eraseBlockSize = "65536";
+          address = lim.parseInt "0xbc050000";
+          size = lim.parseInt "0xfb0000";
+          eraseBlockSize = 65536;
         };
         rootDevice = "/dev/mtdblock5";
 
diff --git a/devices/qemu-aarch64/default.nix b/devices/qemu-aarch64/default.nix
index cc7b07e..cd246b9 100644
--- a/devices/qemu-aarch64/default.nix
+++ b/devices/qemu-aarch64/default.nix
@@ -69,7 +69,7 @@
         entryPoint = lim.parseInt "0x0";
         rootDevice = "/dev/mtdblock0";
 
-        flash.eraseBlockSize = "65536"; # c.f. pkgs/mips-vm/mips-vm.sh
+        flash.eraseBlockSize = 65536; # c.f. pkgs/mips-vm/mips-vm.sh
         networkInterfaces =
           let inherit (config.system.service.network) link;
           in {
diff --git a/devices/qemu-armv7l/default.nix b/devices/qemu-armv7l/default.nix
index 201d39e..6e60849 100644
--- a/devices/qemu-armv7l/default.nix
+++ b/devices/qemu-armv7l/default.nix
@@ -71,7 +71,7 @@
         entryPoint = lim.parseInt "0x00010000";
         rootDevice = "/dev/mtdblock0";
 
-        flash.eraseBlockSize = "65536"; # c.f. pkgs/mips-vm/mips-vm.sh
+        flash.eraseBlockSize = 65536; # c.f. pkgs/mips-vm/mips-vm.sh
         networkInterfaces =
           let inherit (config.system.service.network) link;
           in {
diff --git a/devices/qemu/default.nix b/devices/qemu/default.nix
index b5a2755..87d7b47 100644
--- a/devices/qemu/default.nix
+++ b/devices/qemu/default.nix
@@ -73,7 +73,7 @@
       in {
         defaultOutput = "vmroot";
         rootDevice = "/dev/mtdblock0";
-        flash.eraseBlockSize = "65536"; # c.f. pkgs/run-liminix-vm/run-liminix-vm.sh
+        flash.eraseBlockSize = 65536;
         networkInterfaces =
           let inherit (config.system.service.network) link;
           in {
diff --git a/modules/hardware.nix b/modules/hardware.nix
index 938df1a..81ab050 100644
--- a/modules/hardware.nix
+++ b/modules/hardware.nix
@@ -48,15 +48,15 @@ in {
             kernel uimage and root fs. Usually not the entire flash, as
             we don't want to clobber the bootloader, calibration data etc
           '';
-          type = types.str;
+          type = types.ints.unsigned;
         };
         size = mkOption {
-          type = types.str;
+          type = types.ints.unsigned;
           description = "Size in bytes of the firmware partition";
         };
         eraseBlockSize = mkOption {
           description = "Flash erase block size in bytes";
-          type = types.str;
+          type = types.ints.unsigned;
         };
       };
       loadAddress = mkOption { type = types.ints.unsigned; default = null; };
diff --git a/modules/jffs2.nix b/modules/jffs2.nix
index cb822e6..d85ba26 100644
--- a/modules/jffs2.nix
+++ b/modules/jffs2.nix
@@ -37,7 +37,7 @@ in
           cp ${systemConfiguration}/bin/activate $TMPDIR/empty/activate
           ln -s ${pkgs.s6-init-bin}/bin/init $TMPDIR/empty/init
           grafts=$(sed < ${systemConfiguration}/etc/nix-store-paths 's/^\(.*\)$/--graft \1:\1/g')
-          mkfs.jffs2 --compression-mode=size ${endian} -e ${config.hardware.flash.eraseBlockSize} --enable-compressor=lzo --pad --root $TMPDIR/empty --output $out  $grafts --squash --faketime
+          mkfs.jffs2 --compression-mode=size ${endian} -e ${toString config.hardware.flash.eraseBlockSize} --enable-compressor=lzo --pad --root $TMPDIR/empty --output $out  $grafts --squash --faketime
         '';
     };
   };
diff --git a/modules/outputs/flashimage.nix b/modules/outputs/flashimage.nix
index 42d0bce..41d6a75 100644
--- a/modules/outputs/flashimage.nix
+++ b/modules/outputs/flashimage.nix
@@ -75,7 +75,7 @@ in {
       firmware =
         let
           o = config.system.outputs;
-          bs = config.hardware.flash.eraseBlockSize;
+          bs = toString config.hardware.flash.eraseBlockSize;
         in pkgs.runCommand "firmware" {} ''
           dd if=${o.uimage} of=$out bs=${bs} conv=sync
           dd if=${o.rootfs} of=$out bs=${bs} conv=sync,nocreat,notrunc oflag=append
@@ -107,8 +107,8 @@ in {
             setenv serverip ${tftp.serverip}
             setenv ipaddr ${tftp.ipaddr}
             tftp 0x${toHexString tftp.loadAddress} result/firmware.bin
-            erase 0x$(printf %x ${flash.address}) +${flash.size}
-            cp.b 0x${toHexString tftp.loadAddress} 0x$(printf %x ${flash.address}) \''${filesize}
+            erase 0x${toHexString flash.address} +0x${toHexString flash.size}
+            cp.b 0x${toHexString tftp.loadAddress} 0x${toHexString flash.address} \''${filesize}
             echo command line was ${builtins.toJSON (concatStringsSep " " config.boot.commandLine)}
             EOF
           '';
diff --git a/modules/tftpboot.nix b/modules/tftpboot.nix
index 2c3c879..70bcae0 100644
--- a/modules/tftpboot.nix
+++ b/modules/tftpboot.nix
@@ -74,7 +74,7 @@ in {
             rootfsBytes=$(($(stat -L -c %s ${o.rootfs}) + 0x100000 &(~0xfffff)))
             rootfsBytes=$(($rootfsBytes + ${toString cfg.freeSpaceBytes} ))
             rootfsMb=$(($rootfsBytes >> 20))
-            cmd="mtdparts=phram0:''${rootfsMb}M(rootfs) phram.phram=phram0,''${rootfsStart},''${rootfsBytes},${config.hardware.flash.eraseBlockSize} root=/dev/mtdblock0";
+            cmd="mtdparts=phram0:''${rootfsMb}M(rootfs) phram.phram=phram0,''${rootfsStart},''${rootfsBytes},${toString config.hardware.flash.eraseBlockSize} root=/dev/mtdblock0";
 
             dtbStart=$(printf %x $((${toString cfg.loadAddress} + $rootfsBytes + 0x100000 + $uimageSize )))
 
diff --git a/pkgs/kernel/uimage.nix b/pkgs/kernel/uimage.nix
index e096a91..eca50d5 100644
--- a/pkgs/kernel/uimage.nix
+++ b/pkgs/kernel/uimage.nix
@@ -46,7 +46,7 @@ in {
   buildPhaseUImage = ''
     test -f tmp.dtb && ${objcopy} --update-section .appended_dtb=tmp.dtb vmlinux.elf || ${objcopy} --add-section .appended_dtb=tmp.dtb vmlinux.elf
     ${stripAndZip}
-    mkimage -A ${arch} -O linux -T kernel -C lzma -a 0x${lib.toHexString loadAddress} -e 0x${lib.tohexString entryPoint} -n '${lib.toUpper arch} Liminix Linux ${extraName}' -d vmlinux.bin.lzma kernel.uimage
+    mkimage -A ${arch} -O linux -T kernel -C lzma -a 0x${lib.toHexString loadAddress} -e 0x${lib.toHexString entryPoint} -n '${lib.toUpper arch} Liminix Linux ${extraName}' -d vmlinux.bin.lzma kernel.uimage
   '';
 
   buildPhaseFIT = ''