diff --git a/modules/initrd-contact-info.nix b/modules/initrd-contact-info.nix
index 3d1eba5..6a5ac26 100644
--- a/modules/initrd-contact-info.nix
+++ b/modules/initrd-contact-info.nix
@@ -2,11 +2,47 @@
 
 { config, pkgs, lib, ... }:
 let
+  # TODO: Once `lib.string.trim` is available in stable nix, remove the below.
+  # Copied from https://github.com/NixOS/nixpkgs/blob/5633bcff0c6162b9e4b5f1264264611e950c8ec7/lib/strings.nix#L362-L434
+  trim = trimWith {
+    start = true;
+    end = true;
+  };
+  trimWith =
+    {
+      start ? false,
+      end ? false,
+    }:
+    let
+      # Define our own whitespace character class instead of using
+      # `[:space:]`, which is not well-defined.
+      chars = " \t\r\n";
+
+      # To match up until trailing whitespace, we need to capture a
+      # group that ends with a non-whitespace character.
+      regex =
+        if start && end then
+          "[${chars}]*(.*[^${chars}])[${chars}]*"
+        else if start then
+          "[${chars}]*(.*)"
+        else if end then
+          "(.*[^${chars}])[${chars}]*"
+        else
+          "(.*)";
+    in
+    s:
+    let
+      # If the string was empty or entirely whitespace,
+      # then the regex may not match and `res` will be `null`.
+      res = lib.match regex s;
+    in
+    lib.optionalString (res != null) (lib.head res);
+
   contact_name = "Daniel Langbein";
   # The file `phone-number` contains only one line with our phone number, e.g. +49 0173 ...
   # Be aware that the phone number will be written to the nix store in plaintext!
   # TODO: strip the read string (no tailing newlines)
-  contact_phone = (builtins.readFile ../secrets/phone-number);
+  contact_phone = trim (builtins.readFile ../secrets/phone-number);
   contact_mail = "daniel@systemli.org";
 
   # https://wiki.nixos.org/wiki/Shell_Scripts