diff --git a/app/models/problem_check.rb b/app/models/problem_check.rb
index bc6a7aa37f7..4235ea0759c 100644
--- a/app/models/problem_check.rb
+++ b/app/models/problem_check.rb
@@ -90,6 +90,10 @@ class ProblemCheck
     ProblemCheck::WatchedWords,
   ].freeze
 
+  # To enforce the unique constraint in Postgres <15 we need a dummy
+  # value, since the index considers NULLs to be distinct.
+  NO_TARGET = "__NULL__"
+
   def self.[](key)
     key = key.to_sym
 
@@ -176,12 +180,12 @@ class ProblemCheck
 
   private
 
-  def tracker(target = nil)
+  def tracker(target = NO_TARGET)
     ProblemCheckTracker[identifier, target]
   end
 
   def targets
-    [nil]
+    [NO_TARGET]
   end
 
   def problem(override_key: nil, override_data: {})
diff --git a/app/models/problem_check_tracker.rb b/app/models/problem_check_tracker.rb
index b9ef0054167..4587c296ed4 100644
--- a/app/models/problem_check_tracker.rb
+++ b/app/models/problem_check_tracker.rb
@@ -7,7 +7,7 @@ class ProblemCheckTracker < ActiveRecord::Base
   scope :failing, -> { where("last_problem_at = last_run_at") }
   scope :passing, -> { where("last_success_at = last_run_at") }
 
-  def self.[](identifier, target = nil)
+  def self.[](identifier, target = ProblemCheck::NO_TARGET)
     find_or_create_by(identifier:, target:)
   end
 
@@ -71,11 +71,7 @@ class ProblemCheckTracker < ActiveRecord::Base
   end
 
   def admin_notice
-    if target.present?
-      AdminNotice.problem.where("details->>'target' = ?", target)
-    else
-      AdminNotice.problem.where("(details->>'target') IS NULL")
-    end
+    AdminNotice.problem.where("details->>'target' = ?", target || ProblemCheck::NO_TARGET)
   end
 end
 
@@ -91,7 +87,7 @@ end
 #  last_success_at :datetime
 #  last_problem_at :datetime
 #  details         :json
-#  target          :string
+#  target          :string           default("__NULL__")
 #
 # Indexes
 #
diff --git a/db/migrate/20241018031851_add_default_value_to_problem_check_trackers_target.rb b/db/migrate/20241018031851_add_default_value_to_problem_check_trackers_target.rb
new file mode 100644
index 00000000000..486057f8529
--- /dev/null
+++ b/db/migrate/20241018031851_add_default_value_to_problem_check_trackers_target.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+class AddDefaultValueToProblemCheckTrackersTarget < ActiveRecord::Migration[7.1]
+  def up
+    change_column_default :problem_check_trackers, :target, "__NULL__"
+
+    execute(<<~SQL)
+      UPDATE problem_check_trackers
+      SET target='__NULL__'
+      WHERE target IS NULL
+    SQL
+  end
+
+  def down
+    change_column_default :problem_check_trackers, :target, nil
+
+    execute(<<~SQL)
+      UPDATE problem_check_trackers
+      SET target = NULL
+      WHERE target = '__NULL__'
+    SQL
+  end
+end
diff --git a/spec/models/problem_check_tracker_spec.rb b/spec/models/problem_check_tracker_spec.rb
index 9b07d47ecb4..dadeca7bb6f 100644
--- a/spec/models/problem_check_tracker_spec.rb
+++ b/spec/models/problem_check_tracker_spec.rb
@@ -187,7 +187,6 @@ RSpec.describe ProblemCheckTracker do
       before { ProblemCheck::TwitterLogin.stubs(:max_blips).returns(1) }
 
       it "does not sound the alarm" do
-        puts ProblemCheck::TwitterLogin.max_blips
         expect { problem_tracker.problem!(next_run_at: 24.hours.from_now) }.not_to change {
           AdminNotice.problem.count
         }
@@ -221,7 +220,7 @@ RSpec.describe ProblemCheckTracker do
     end
 
     context "when there's an alarm sounding" do
-      before { Fabricate(:admin_notice, subject: "problem", identifier: "twitter_login") }
+      before { problem_tracker.problem! }
 
       it "silences the alarm" do
         expect { problem_tracker.no_problem!(next_run_at: 24.hours.from_now) }.to change {