diff --git a/spec/services/staff_action_logger_spec.rb b/spec/services/staff_action_logger_spec.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 RSpec.describe StaffActionLogger do
+  let(:long_string) { "Na " * 100_000 + "Batman!" }
   fab!(:admin)
   let(:logger) { described_class.new(admin) }
 
@@ -69,6 +70,13 @@
         log_post_deletion
       }.to change { UserHistory.count }.by(1)
     end
+
+    it "truncates overly long values" do
+      deleted_post.update!(raw: long_string, skip_validation: true)
+      expect { log_post_deletion }.to change { UserHistory.count }.by(1)
+      log = UserHistory.last
+      expect(log.details.size).to be_between(50_000, 110_000)
+    end
   end
 
   describe "log_topic_delete_recover" do
@@ -90,6 +98,13 @@
       it "creates a new UserHistory record" do
         expect { log_topic_delete_recover }.to change { UserHistory.count }.by(1)
       end
+
+      it "truncates overly long values" do
+        Fabricate(:post, topic: topic, skip_validation: true, raw: long_string)
+        expect { log_topic_delete_recover }.to change { UserHistory.count }.by(1)
+        log = UserHistory.last
+        expect(log.details.size).to be_between(50_000, 110_000)
+      end
     end
 
     context "when recovering topic" do
@@ -112,6 +127,13 @@
       it "creates a new UserHistory record" do
         expect { log_topic_delete_recover }.to change { UserHistory.count }.by(1)
       end
+
+      it "truncates overly long values" do
+        Fabricate(:post, topic: topic, skip_validation: true, raw: long_string)
+        expect { log_topic_delete_recover }.to change { UserHistory.count }.by(1)
+        log = UserHistory.last
+        expect(log.details.size).to be_between(50_000, 110_000)
+      end
     end
   end
 
@@ -187,14 +209,12 @@
   end
 
   describe "log_theme_change" do
+    fab!(:theme)
+
     it "raises an error when params are invalid" do
       expect { logger.log_theme_change(nil, nil) }.to raise_error(Discourse::InvalidParameters)
     end
 
-    let! :theme do
-      Fabricate(:theme)
-    end
-
     it "logs new site customizations" do
       log_record = logger.log_theme_change(nil, theme)
       expect(log_record.subject).to eq(theme.name)
@@ -226,15 +246,28 @@
         ],
       )
     end
+
+    it "doesn't log values when the json is too large" do
+      old_json = ThemeSerializer.new(theme, root: false).to_json
+
+      theme.set_field(target: :common, name: :scss, value: long_string)
+
+      log_record = logger.log_theme_change(old_json, theme)
+
+      expect(log_record.previous_value).not_to be_present
+      expect(log_record.new_value).not_to be_present
+      expect(log_record.context).to be_present
+    end
   end
 
   describe "log_theme_destroy" do
+    fab!(:theme)
+
     it "raises an error when params are invalid" do
       expect { logger.log_theme_destroy(nil) }.to raise_error(Discourse::InvalidParameters)
     end
 
     it "creates a new UserHistory record" do
-      theme = Fabricate(:theme)
       theme.set_field(target: :common, name: :scss, value: "body{margin: 10px;}")
 
       log_record = logger.log_theme_destroy(theme)
@@ -253,6 +286,15 @@
         ],
       )
     end
+
+    it "doesn't log values when the json is too large" do
+      theme.set_field(target: :common, name: :scss, value: long_string)
+      log_record = logger.log_theme_destroy(theme)
+
+      expect(log_record.previous_value).not_to be_present
+      expect(log_record.new_value).not_to be_present
+      expect(log_record.context).to be_present
+    end
   end
 
   describe "log_theme_setting_change" do
@@ -398,6 +440,12 @@
       expect(logged.custom_type).to eq("clicked_something")
       expect(logged.topic_id).to be === 1234
     end
+
+    it "truncates overly long values" do
+      logged = logger.log_custom(:shower_thought, lyrics: long_string)
+      expect(logged).to be_valid
+      expect(logged.details.size).to be_between(50_000, 110_000)
+    end
   end
 
   describe "log_category_settings_change" do
@@ -654,6 +702,15 @@
       expect(user_history.action).to eq(UserHistory.actions[:post_rejected])
       expect(user_history.details).to include(reviewable.payload["raw"])
     end
+
+    it "truncates overly long values" do
+      reviewable.payload["raw"] = long_string
+      reviewable.save!
+
+      expect { log_post_rejected }.to change { UserHistory.count }.by(1)
+      log = UserHistory.last
+      expect(log.details.size).to be_between(50_000, 110_000)
+    end
   end
 
   describe "log_topic_closed" do