diff --git a/modules/programs/bash/bash.nix b/modules/programs/bash/bash.nix
index dc36ab7d97f..31a14663aa0 100644
--- a/modules/programs/bash/bash.nix
+++ b/modules/programs/bash/bash.nix
@@ -15,7 +15,7 @@ let
         description = "
           Script used to initialized user shell environments.
         ";
-        merge = mergeStringOption;
+        type = with pkgs.lib.types; string;
       };
 
   };
diff --git a/modules/services/hardware/udev.nix b/modules/services/hardware/udev.nix
index 55f830c5365..6caac8f8ca2 100644
--- a/modules/services/hardware/udev.nix
+++ b/modules/services/hardware/udev.nix
@@ -170,7 +170,7 @@ in
         example = ''
           KERNEL=="eth*", ATTR{address}=="00:1D:60:B9:6D:4F", NAME="my_fast_network_card"
         '';
-        merge = mergeStringOption;
+        type = with pkgs.lib.types; string;
         description = ''
           Additional <command>udev</command> rules. They'll be written
           into file <filename>10-local.rules</filename>. Thus they are
diff --git a/modules/services/misc/nix-daemon.nix b/modules/services/misc/nix-daemon.nix
index c8eaf15ff77..d2584c2dc3e 100644
--- a/modules/services/misc/nix-daemon.nix
+++ b/modules/services/misc/nix-daemon.nix
@@ -171,7 +171,7 @@ in
       envVars = mkOption {
         internal = true;
         default = "";
-        merge = mergeStringOption;
+        type = with pkgs.lib.types; string;
         description = "
           Environment variables used by Nix.
         ";
diff --git a/modules/system/boot/stage-1.nix b/modules/system/boot/stage-1.nix
index e178f2c04c9..bc27c9f80ff 100644
--- a/modules/system/boot/stage-1.nix
+++ b/modules/system/boot/stage-1.nix
@@ -37,7 +37,7 @@ let
 
     boot.initrd.preLVMCommands = mkOption {
       default = "";
-      merge = mergeStringOption;
+      type = with types; string;
       description = ''
         Shell commands to be executed immediately before lvm discovery.
       '';
@@ -45,7 +45,7 @@ let
 
     boot.initrd.postDeviceCommands = mkOption {
       default = "";
-      merge = mergeStringOption;
+      type = with types; string;
       description = ''
         Shell commands to be executed immediately after stage 1 of the
         boot has loaded kernel modules and created device nodes in
@@ -55,7 +55,7 @@ let
 
     boot.initrd.postMountCommands = mkOption {
       default = "";
-      merge = mergeStringOption;
+      type = with types; string;
       description = ''
         Shell commands to be executed immediately after the stage 1
         filesystems have been mounted.
@@ -65,7 +65,7 @@ let
     boot.initrd.extraUtilsCommands = mkOption {
       internal = true;
       default = "";
-      merge = mergeStringOption;
+      type = with types; string;
       description = ''
         Shell commands to be executed in the builder of the
         extra-utils derivation.  This can be used to provide
@@ -76,7 +76,7 @@ let
     boot.initrd.extraUtilsCommandsTest = mkOption {
       internal = true;
       default = "";
-      merge = mergeStringOption;
+      type = with types; string;
       description = ''
         Shell commands to be executed in the builder of the
         extra-utils derivation after patchelf has done its
diff --git a/modules/system/boot/stage-2.nix b/modules/system/boot/stage-2.nix
index 1fb8379f29a..c45dc348b66 100644
--- a/modules/system/boot/stage-2.nix
+++ b/modules/system/boot/stage-2.nix
@@ -8,7 +8,7 @@ let
       postBootCommands = pkgs.lib.mkOption {
         default = "";
         example = "rm -f /var/log/messages";
-        merge = pkgs.lib.mergeStringOption;
+        type = with pkgs.lib.types; string;
         description = ''
           Shell commands to be executed just before Upstart is started.
         '';