diff --git a/modules/nix/default.nix b/modules/nix/default.nix
index 2588d3be..528c304a 100644
--- a/modules/nix/default.nix
+++ b/modules/nix/default.nix
@@ -37,7 +37,7 @@ let
         if v == null then ""
         else if isInt v then toString v
         else if isBool v then boolToString v
-        else if isFloat v then floatToString v
+        else if isFloat v then strings.floatToString v
         else if isList v then toString v
         else if isDerivation v then toString v
         else if builtins.isPath v then toString v
diff --git a/modules/system/defaults-write.nix b/modules/system/defaults-write.nix
index 37e6760c..8a6cb6ea 100644
--- a/modules/system/defaults-write.nix
+++ b/modules/system/defaults-write.nix
@@ -5,14 +5,12 @@ with lib;
 let
   cfg = config.system.defaults;
 
-  isFloat = x: isString x && builtins.match "^[+-]?([0-9]*[.])?[0-9]+$" x != null;
-
   boolValue = x: if x then "YES" else "NO";
 
   writeValue = value:
     if isBool value then "-bool ${boolValue value}" else
     if isInt value then "-int ${toString value}" else
-    if isFloat value then "-float ${toString value}" else
+    if isFloat value then "-float ${strings.floatToString value}" else
     if isString value then "-string '${value}'" else
     throw "invalid value type";
 
@@ -48,6 +46,15 @@ in
 {
   config = {
 
+    # Type used for `system.defaults.<domain>.*` options that previously accepted float values as a
+    # string.
+    lib.defaults.types.floatWithDeprecationError = types.float // {
+      check = x:
+        if isString x && builtins.match "^[+-]?([0-9]*[.])?[0-9]+$" x != null
+        then throw "Using strings for `system.defaults.<domain>.*' options of type float is no longer permitted, use native float values instead."
+        else types.float.check x;
+    };
+
     system.activationScripts.defaults.text = mkIfAttrs [
       alf
       loginwindow
diff --git a/modules/system/defaults/NSGlobalDomain.nix b/modules/system/defaults/NSGlobalDomain.nix
index 023c06c5..49a2a865 100644
--- a/modules/system/defaults/NSGlobalDomain.nix
+++ b/modules/system/defaults/NSGlobalDomain.nix
@@ -3,15 +3,8 @@
 with lib;
 
 let
-  isFloat = x: isString x && builtins.match "^[+-]?([0-9]*[.])?[0-9]+$" x != null;
-
-  float = mkOptionType {
-    name = "float";
-    description = "float";
-    check = isFloat;
-    merge = options.mergeOneOption;
-  };
-
+  # Should only be used with options that previously used floats defined as strings.
+  inherit (config.lib.defaults.types) floatWithDeprecationError;
 in {
   options = {
 
@@ -208,9 +201,9 @@ in {
     };
 
     system.defaults.NSGlobalDomain.NSWindowResizeTime = mkOption {
-      type = types.nullOr float;
+      type = types.nullOr floatWithDeprecationError;
       default = null;
-      example = "0.20";
+      example = 0.20;
       description = ''
         Sets the speed speed of window resizing. The default is given in the example.
       '';
@@ -273,14 +266,16 @@ in {
     };
 
     system.defaults.NSGlobalDomain."com.apple.sound.beep.volume" = mkOption {
-      type = types.nullOr float;
+      type = types.nullOr floatWithDeprecationError;
       default = null;
       description = ''
         # Apple menu > System Preferences > Sound
         Sets the beep/alert volume level from 0.000 (muted) to 1.000 (100% volume).
 
         75% = 0.7788008
+
         50% = 0.6065307
+
         25% = 0.4723665
       '';
     };
@@ -312,7 +307,7 @@ in {
     };
 
     system.defaults.NSGlobalDomain."com.apple.trackpad.scaling" = mkOption {
-      type = types.nullOr float;
+      type = types.nullOr floatWithDeprecationError;
       default = null;
       description = ''
         Configures the trackpad tracking speed (0 to 3).  The default is "1".
@@ -328,9 +323,9 @@ in {
     };
 
     system.defaults.NSGlobalDomain."com.apple.springing.delay" = mkOption {
-      type = types.nullOr float;
+      type = types.nullOr floatWithDeprecationError;
       default = null;
-      example = "1.0";
+      example = 1.0;
       description = ''
         Set the spring loading delay for directories. The default is given in the example.
       '';
diff --git a/modules/system/defaults/dock.nix b/modules/system/defaults/dock.nix
index 3156e90a..ba62e7a4 100644
--- a/modules/system/defaults/dock.nix
+++ b/modules/system/defaults/dock.nix
@@ -3,15 +3,8 @@
 with lib;
 
 let
-  isFloat = x: isString x && builtins.match "^[+-]?([0-9]*[.])?[0-9]+$" x != null;
-
-  float = mkOptionType {
-    name = "float";
-    description = "float";
-    check = isFloat;
-    merge = options.mergeOneOption;
-  };
-
+  # Should only be used with options that previously used floats defined as strings.
+  inherit (config.lib.defaults.types) floatWithDeprecationError;
 in {
   options = {
 
@@ -32,18 +25,18 @@ in {
     };
 
     system.defaults.dock.autohide-delay = mkOption {
-      type = types.nullOr float;
+      type = types.nullOr floatWithDeprecationError;
       default = null;
-      example = "0.24";
+      example = 0.24;
       description = ''
         Sets the speed of the autohide delay. The default is given in the example.
       '';
     };
 
     system.defaults.dock.autohide-time-modifier = mkOption {
-      type = types.nullOr float;
+      type = types.nullOr floatWithDeprecationError;
       default = null;
-      example = "1.0";
+      example = 1.0;
       description = ''
         Sets the speed of the animation when hiding/showing the Dock. The default is given in the example.
       '';
@@ -66,9 +59,9 @@ in {
     };
 
     system.defaults.dock.expose-animation-duration = mkOption {
-      type = types.nullOr float;
+      type = types.nullOr floatWithDeprecationError;
       default = null;
-      example = "1.0";
+      example = 1.0;
       description = ''
         Sets the speed of the Mission Control animations. The default is given in the example.
       '';
diff --git a/tests/system-defaults-write.nix b/tests/system-defaults-write.nix
index 821e3402..6a97a410 100644
--- a/tests/system-defaults-write.nix
+++ b/tests/system-defaults-write.nix
@@ -23,7 +23,7 @@
   system.defaults.NSGlobalDomain.NSTextShowsControlCharacters = true;
   system.defaults.NSGlobalDomain.NSUseAnimatedFocusRing = false;
   system.defaults.NSGlobalDomain.NSScrollAnimationEnabled = true;
-  system.defaults.NSGlobalDomain.NSWindowResizeTime = "0.01";
+  system.defaults.NSGlobalDomain.NSWindowResizeTime = 0.01;
   system.defaults.NSGlobalDomain.InitialKeyRepeat = 10;
   system.defaults.NSGlobalDomain.KeyRepeat = 1;
   system.defaults.NSGlobalDomain.PMPrintingExpandedStateForPrint = true;
@@ -33,11 +33,11 @@
   system.defaults.NSGlobalDomain."com.apple.trackpad.enableSecondaryClick" = true;
   system.defaults.NSGlobalDomain."com.apple.trackpad.trackpadCornerClickBehavior" = 1;
   system.defaults.NSGlobalDomain."com.apple.springing.enabled" = true;
-  system.defaults.NSGlobalDomain."com.apple.springing.delay" = "0.0";
+  system.defaults.NSGlobalDomain."com.apple.springing.delay" = 0.0;
   system.defaults.NSGlobalDomain."com.apple.swipescrolldirection" = true;
   system.defaults.".GlobalPreferences"."com.apple.sound.beep.sound" = "/System/Library/Sounds/Funk.aiff";
   system.defaults.dock.appswitcher-all-displays = false;
-  system.defaults.dock.autohide-delay = "0.24";
+  system.defaults.dock.autohide-delay = 0.24;
   system.defaults.dock.orientation = "left";
   system.defaults.screencapture.location = "/tmp";
   system.defaults.smb.NetBIOSName = "IMAC-000000";