diff --git a/app/models/censor_rule.rb b/app/models/censor_rule.rb
index 0ecd281508..4548f21b2c 100644
--- a/app/models/censor_rule.rb
+++ b/app/models/censor_rule.rb
@@ -1,5 +1,5 @@
 # == Schema Information
-# Schema version: 20210114161442
+# Schema version: 20240313094449
 #
 # Table name: censor_rules
 #
@@ -13,7 +13,7 @@
 #  last_edit_comment :text             not null
 #  created_at        :datetime         not null
 #  updated_at        :datetime         not null
-#  regexp            :boolean
+#  regexp            :boolean          default(FALSE), not null
 #
 
 # models/censor_rule.rb:
diff --git a/db/migrate/20240313094449_add_not_null_constraint_to_censor_rule_regexp.rb b/db/migrate/20240313094449_add_not_null_constraint_to_censor_rule_regexp.rb
new file mode 100644
index 0000000000..650f2e6cfa
--- /dev/null
+++ b/db/migrate/20240313094449_add_not_null_constraint_to_censor_rule_regexp.rb
@@ -0,0 +1,12 @@
+class AddNotNullConstraintToCensorRuleRegexp < ActiveRecord::Migration[7.0]
+  def up
+    change_column_default :censor_rules, :regexp, false
+    CensorRule.where(regexp: nil).update_all(regexp: false)
+    change_column_null :censor_rules, :regexp, false
+  end
+
+  def down
+    change_column_null :censor_rules, :regexp, true
+    change_column_default :censor_rules, :regexp, nil
+  end
+end
diff --git a/doc/CHANGES.md b/doc/CHANGES.md
index 4bd9745911..9210750847 100644
--- a/doc/CHANGES.md
+++ b/doc/CHANGES.md
@@ -2,6 +2,7 @@
 
 ## Highlighted Features
 
+* Add default value and not null constraint to `CensorRule#regexp` (Gareth Rees)
 * Reduce amount of storage related background jobs (Graeme Porteous)
 * Add automatic parsing of emails contain Excel spreadsheets (Graeme Porteous)
 * Improve rendering of admin hidden request prominence and explanations (Graeme
diff --git a/spec/factories/censor_rules.rb b/spec/factories/censor_rules.rb
index 3ebe63c206..e9e3ad4f46 100644
--- a/spec/factories/censor_rules.rb
+++ b/spec/factories/censor_rules.rb
@@ -1,5 +1,5 @@
 # == Schema Information
-# Schema version: 20210114161442
+# Schema version: 20240313094449
 #
 # Table name: censor_rules
 #
@@ -13,7 +13,7 @@
 #  last_edit_comment :text             not null
 #  created_at        :datetime         not null
 #  updated_at        :datetime         not null
-#  regexp            :boolean
+#  regexp            :boolean          default(FALSE), not null
 #
 
 FactoryBot.define do
diff --git a/spec/models/censor_rule_spec.rb b/spec/models/censor_rule_spec.rb
index 7d7d923079..04de33231d 100644
--- a/spec/models/censor_rule_spec.rb
+++ b/spec/models/censor_rule_spec.rb
@@ -1,5 +1,5 @@
 # == Schema Information
-# Schema version: 20210114161442
+# Schema version: 20240313094449
 #
 # Table name: censor_rules
 #
@@ -13,7 +13,7 @@
 #  last_edit_comment :text             not null
 #  created_at        :datetime         not null
 #  updated_at        :datetime         not null
-#  regexp            :boolean
+#  regexp            :boolean          default(FALSE), not null
 #
 
 require 'spec_helper'