diff --git a/devices/belkin-rt3200/default.nix b/devices/belkin-rt3200/default.nix
index 218bcff..c226e8a 100644
--- a/devices/belkin-rt3200/default.nix
+++ b/devices/belkin-rt3200/default.nix
@@ -38,7 +38,7 @@
     };
   };
 
-  module = {pkgs, config, lib, ... }:
+  module = {pkgs, config, lib, lim, ... }:
     let firmware = pkgs.stdenv.mkDerivation {
           name = "wlan-firmware";
           phases = ["installPhase"];
@@ -143,7 +143,7 @@
     };
     boot = {
       commandLine = [ "console=ttyS0,115200" ];
-      tftp.loadAddress =  "0x4007ff28";
+      tftp.loadAddress = lim.parseInt "0x4007ff28";
       imageFormat = "fit";
     };
     filesystem =
diff --git a/devices/gl-ar750/default.nix b/devices/gl-ar750/default.nix
index 068a147..aba6030 100644
--- a/devices/gl-ar750/default.nix
+++ b/devices/gl-ar750/default.nix
@@ -144,7 +144,7 @@
         };
       };
       boot.tftp = {
-        loadAddress = "0x00A00000";
+        loadAddress = lim.parseInt "0x00A00000";
       };
       kernel = {
         src = pkgs.pkgsBuildBuild.fetchurl {
diff --git a/devices/gl-mt300a/default.nix b/devices/gl-mt300a/default.nix
index d796560..55ae68c 100644
--- a/devices/gl-mt300a/default.nix
+++ b/devices/gl-mt300a/default.nix
@@ -43,7 +43,7 @@
 
   '';
 
-  module = { pkgs, config, lib, ...}:
+  module = { pkgs, config, lib, lim, ...}:
     let
       inherit (pkgs.liminix.networking) interface;
       inherit (pkgs) openwrt;
@@ -120,7 +120,7 @@
           };
       };
       boot.tftp = {
-        loadAddress = "0x00A00000";
+        loadAddress = lim.parseInt "0x00A00000";
       };
 
       kernel = {
diff --git a/devices/gl-mt300n-v2/default.nix b/devices/gl-mt300n-v2/default.nix
index 21dc336..be3c4a6 100644
--- a/devices/gl-mt300n-v2/default.nix
+++ b/devices/gl-mt300n-v2/default.nix
@@ -36,7 +36,7 @@
 
   '';
 
-  module = { pkgs, config, lib, ...}:
+  module = { pkgs, config, lib, lim, ...}:
     let
       inherit (pkgs.liminix.networking) interface;
       inherit (pkgs.liminix.services) oneshot;
@@ -116,7 +116,7 @@
       boot.tftp = {
         # 20MB seems to give enough room to uncompress the kernel
         # without anything getting trodden on. 10MB was too small
-        loadAddress = "0x1400000";
+        loadAddress = lim.parseInt "0x1400000";
       };
 
       kernel = {
diff --git a/modules/base.nix b/modules/base.nix
index 75bb3b3..521bfb2 100644
--- a/modules/base.nix
+++ b/modules/base.nix
@@ -58,7 +58,7 @@ in {
       };
       tftp = {
         loadAddress = mkOption {
-          type = types.str;
+          type = types.ints.unsigned;
           description = ''
             RAM address at which to load data when transferring via
             TFTP. This is not the address of the flash storage,
diff --git a/modules/outputs/flashimage.nix b/modules/outputs/flashimage.nix
index 73967d7..42d0bce 100644
--- a/modules/outputs/flashimage.nix
+++ b/modules/outputs/flashimage.nix
@@ -106,9 +106,9 @@ in {
             cat > $out << EOF
             setenv serverip ${tftp.serverip}
             setenv ipaddr ${tftp.ipaddr}
-            tftp 0x$(printf %x ${tftp.loadAddress}) result/firmware.bin
+            tftp 0x${toHexString tftp.loadAddress} result/firmware.bin
             erase 0x$(printf %x ${flash.address}) +${flash.size}
-            cp.b 0x$(printf %x ${tftp.loadAddress}) 0x$(printf %x ${flash.address}) \''${filesize}
+            cp.b 0x${toHexString tftp.loadAddress} 0x$(printf %x ${flash.address}) \''${filesize}
             echo command line was ${builtins.toJSON (concatStringsSep " " config.boot.commandLine)}
             EOF
           '';