diff --git a/config/runtime.exs b/config/runtime.exs
index 223a46e..904f4f7 100644
--- a/config/runtime.exs
+++ b/config/runtime.exs
@@ -67,15 +67,6 @@ if config_env() == :prod do
   # For running PF in a subdirectory via a reverse proxy
   base_route_path = System.get_env("BASE_ROUTE_PATH", "/")
   enable_ipv6 = String.length(System.get_env("ENABLE_IPV6", "")) > 0
-  attempted_timezone = System.get_env("TIMEZONE") || System.get_env("TZ") || "UTC"
-
-  valid_timezone =
-    if Timex.Timezone.exists?(attempted_timezone) do
-      attempted_timezone
-    else
-      Logger.warning("Invalid timezone #{attempted_timezone}, defaulting to UTC")
-      "UTC"
-    end
 
   config :logger, level: String.to_existing_atom(System.get_env("LOG_LEVEL", "debug"))
 
@@ -88,7 +79,8 @@ if config_env() == :prod do
     tmpfile_directory: Path.join([System.tmp_dir!(), "pinchflat", "data"]),
     dns_cluster_query: System.get_env("DNS_CLUSTER_QUERY"),
     expose_feed_endpoints: expose_feed_endpoints,
-    timezone: valid_timezone,
+    # This is configured in application.ex
+    timezone: "UTC",
     log_path: log_path,
     base_route_path: base_route_path
 
diff --git a/lib/pinchflat/application.ex b/lib/pinchflat/application.ex
index 49adcf0..61b2538 100644
--- a/lib/pinchflat/application.ex
+++ b/lib/pinchflat/application.ex
@@ -4,9 +4,12 @@ defmodule Pinchflat.Application do
   @moduledoc false
 
   use Application
+  require Logger
 
   @impl true
   def start(_type, _args) do
+    check_and_update_timezone()
+
     children = [
       PinchflatWeb.Telemetry,
       Pinchflat.Repo,
@@ -47,4 +50,20 @@ defmodule Pinchflat.Application do
     :ok = Oban.Telemetry.attach_default_logger()
     :telemetry.attach_many("job-telemetry-broadcast", events, &PinchflatWeb.Telemetry.job_state_change_broadcast/4, [])
   end
+
+  # This has to be here (rather than runtime.exs) since the `tzdata` application
+  # has to be started before we can check the timezone
+  defp check_and_update_timezone do
+    attempted_timezone = System.get_env("TIMEZONE") || System.get_env("TZ") || "UTC"
+
+    valid_timezone =
+      if Tzdata.zone_exists?(attempted_timezone) do
+        attempted_timezone
+      else
+        Logger.warning("Invalid timezone #{attempted_timezone}, defaulting to UTC")
+        "UTC"
+      end
+
+    Application.put_env(:pinchflat, :timezone, valid_timezone)
+  end
 end