diff --git a/db/migrate/20220406072625_coerce_timezones.rb b/db/migrate/20220406072625_coerce_timezones.rb
new file mode 100644
index 00000000..86bdccd2
--- /dev/null
+++ b/db/migrate/20220406072625_coerce_timezones.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+# Normalizes values in tzinfo_tz
+class CoerceTimezones < ActiveRecord::Migration[7.0]
+  def migrate_tzinfo_tz(target_table)
+    # execute raw queries - we don't want our models triggering updates or hooks
+
+    # first fetch all rows
+    results = ActiveRecord::Base.connection.execute(
+      <<~SQL
+        SELECT id, tzinfo_tz FROM #{target_table};
+      SQL
+    )
+
+    # then resolve timezone
+    results.each { |row|
+      id = row['id']
+      old = row['tzinfo_tz']
+
+      case old
+      when nil, '' then nil
+      # special case the one value we can't automatically infer
+      when 'UTC -2' then 'Etc/GMT-2'
+      else TimeZoneHelper.to_identifier(row['tzinfo_tz'])
+      end => found
+
+      # and then update the values
+      value = found.nil? ? 'NULL' : "'#{found}'"
+      update_query = <<~SQL
+        UPDATE #{target_table}
+        SET tzinfo_tz = #{value}
+        WHERE id = #{row['id']};
+      SQL
+
+      Rails.logger.warn('Data migration executing', id:, old:, found:, update_query:)
+
+      execute(update_query)
+    }
+  end
+
+  def change
+    reversible do |change|
+      change.up do
+        migrate_tzinfo_tz(:users)
+        migrate_tzinfo_tz(:sites)
+      end
+
+      change.down do
+        Rails.logger.warn(
+          'This migration is backwards compatible but does not support reverse migration - no data has been changed'
+        )
+      end
+    end
+  end
+end
diff --git a/spec/migrations/coerce_timezones_spec.rb b/spec/migrations/coerce_timezones_spec.rb
new file mode 100644
index 00000000..b82a9f20
--- /dev/null
+++ b/spec/migrations/coerce_timezones_spec.rb
@@ -0,0 +1,113 @@
+# frozen_string_literal: true
+
+require_migration!
+
+# So we're testing a data migration.
+# Actually using the tzinfo_tz column in queries now has resulted in invalid timezones in our database
+# becoming a major issue.
+# We're adding a migration to deal with this, these are the tests.
+describe CoerceTimezones, :migration do
+  # Format old, expected value after migration
+  # These examples were taken directly from a production database
+  CASES = [
+    ['Asia - Dhaka', 'Asia/Dhaka'],
+    ['UTC -2', 'Etc/GMT-2'],
+    ['Pacific - Port Moresby', 'Pacific/Port_Moresby'],
+    ['Australia - Sydney', 'Australia/Sydney'],
+    ['Australia/Adelaide', 'Australia/Adelaide'],
+    ['Australia/Brisbane', 'Australia/Brisbane'],
+    ['Australia/Sydney', 'Australia/Sydney'],
+    ['Australia - Melbourne', 'Australia/Melbourne'],
+    ['US - Eastern', 'US/Eastern'],
+    [nil, nil],
+    ['Australia - NSW', 'Australia/NSW'],
+    ['Asia - Singapore', 'Asia/Singapore'],
+    ['America - Costa Rica', 'America/Costa_Rica'],
+    ['Asia - Yangon', 'Asia/Yangon'],
+    ['Asia - Thimphu', 'Asia/Thimphu'],
+    ['Australia - Tasmania', 'Australia/Tasmania'],
+    ['Australia - Darwin', 'Australia/Darwin'],
+    ['Asia - Makassar', 'Asia/Makassar'],
+    ['America - Bogota', 'America/Bogota'],
+    ['Europe - Berlin', 'Europe/Berlin'],
+    ['Australia/Melbourne', 'Australia/Melbourne'],
+    ['Australia - Adelaide', 'Australia/Adelaide'],
+    ['America - Lima', 'America/Lima'],
+    ['Australia - Hobart', 'Australia/Hobart'],
+    ['', nil],
+    ['Australia - Brisbane', 'Australia/Brisbane'],
+    ['Asia - Bangkok', 'Asia/Bangkok']
+  ].freeze
+
+  before do
+    user_values = ''
+    site_values = ''
+    CASES.each_with_index do |example, index|
+      delimit = index == CASES.length - 1 ? '' : ",\n"
+      example => [bad_value, _good_value]
+      user_values += "(#{index}, 'user #{index}', 'user#{index}@example.com', 'boogers', '#{bad_value}')#{delimit}"
+      site_values += "(#{index}, 'site #{index}', #{index}, '#{bad_value}')#{delimit}"
+    end
+
+    # We have corrective code for this problem already in our models
+    # we avoid active record and execute raw queries instead
+    ActiveRecord::Base.connection.execute(
+      <<~SQL
+        DELETE FROM datasets;
+        DELETE FROM sites;
+        DELETE FROM users;
+
+        INSERT INTO users (id, user_name, email, encrypted_password, tzinfo_tz)
+        VALUES #{user_values};
+
+        INSERT INTO sites (id, name, creator_id, tzinfo_tz)
+        VALUES #{site_values};
+      SQL
+    )
+
+    expect(User.count).to eq CASES.length
+    expect(Site.count).to eq CASES.length
+  end
+
+  it 'migrates data correctly for sites' do
+    migrate!
+
+    # again execute raw query to avoid corrective code
+    results = ActiveRecord::Base.connection.execute(
+      <<~SQL
+        SELECT id, tzinfo_tz FROM sites ORDER BY id ASC;
+      SQL
+    )
+
+    # after migration everything should be nice
+    aggregate_failures do
+      CASES.each_with_index do |example, index|
+        example => [bad_value, good_value]
+
+        actual = results[index]['tzinfo_tz']
+        expect(actual).to eq(good_value)
+      end
+    end
+  end
+
+  it 'migrates data correctly for users' do
+    migrate!
+
+    # again execute raw query to avoid corrective code
+    results = ActiveRecord::Base.connection.execute(
+      <<~SQL
+        SELECT id, tzinfo_tz FROM users ORDER BY id ASC;
+      SQL
+    )
+
+    # after migration everything should be nice
+    aggregate_failures do
+      CASES.each_with_index do |example, index|
+        example => [bad_value, good_value]
+
+        actual = results[index]['tzinfo_tz']
+        expect(actual).to eq(good_value)
+      end
+    end
+  end
+end