diff --git a/config/locales/server.en.yml b/config/locales/server.en.yml
index 51fbcc0235a..ea615b65554 100644
--- a/config/locales/server.en.yml
+++ b/config/locales/server.en.yml
@@ -169,6 +169,7 @@ en:
       default_categories_already_selected: "You cannot select a category used in another list."
       s3_upload_bucket_is_required: "You cannot enable uploads to S3 unless you've provided the 's3_upload_bucket'."
       s3_backup_requires_s3_settings: "You cannot use S3 as backup location unless you've provided the '%{setting_name}'."
+      s3_bucket_reused: "You cannot use the same bucket for 's3_upload_bucket' and 's3_backup_bucket'. Choose a different bucket or use a different path for each bucket."
     conflicting_google_user_id: 'The Google Account ID for this account has changed; staff intervention is required for security reasons. Please contact staff and point them to <br><a href="https://meta.discourse.org/t/76575">https://meta.discourse.org/t/76575</a>'
 
   activemodel:
@@ -190,7 +191,7 @@ en:
     error: "There was an error uploading that file. Please try again later."
 
   topic_invite:
-    failed_to_invite: "The user cannot be invited into this topic without a group membership in either one of the following groups: %{group_names}." 
+    failed_to_invite: "The user cannot be invited into this topic without a group membership in either one of the following groups: %{group_names}."
     user_exists: "Sorry, that user has already been invited. You may only invite a user to a topic once."
 
   backup:
diff --git a/lib/site_settings/validations.rb b/lib/site_settings/validations.rb
index 0d50f488b3d..2d03fefc3cf 100644
--- a/lib/site_settings/validations.rb
+++ b/lib/site_settings/validations.rb
@@ -62,4 +62,33 @@ module SiteSettings::Validations
       validate_error(:s3_backup_requires_s3_settings, setting_name: "s3_secret_access_key") if SiteSetting.s3_secret_access_key.blank?
     end
   end
+
+  def validate_s3_upload_bucket(new_val)
+    validate_bucket_setting("s3_upload_bucket", new_val, SiteSetting.s3_backup_bucket)
+  end
+
+  def validate_s3_backup_bucket(new_val)
+    validate_bucket_setting("s3_backup_bucket", SiteSetting.s3_upload_bucket, new_val)
+  end
+
+  private
+
+  def validate_bucket_setting(setting_name, upload_bucket, backup_bucket)
+    return if upload_bucket.blank? || backup_bucket.blank?
+
+    backup_bucket_name, backup_prefix = split_s3_bucket(backup_bucket)
+    upload_bucket_name, upload_prefix = split_s3_bucket(upload_bucket)
+
+    return if backup_bucket_name != upload_bucket_name
+
+    if backup_prefix == upload_prefix || backup_prefix.blank? || upload_prefix&.start_with?(backup_prefix)
+      validate_error(:s3_bucket_reused, setting_name: setting_name)
+    end
+  end
+
+  def split_s3_bucket(s3_bucket)
+    bucket_name, prefix = s3_bucket.downcase.split("/", 2)
+    prefix&.chomp!("/")
+    [bucket_name, prefix]
+  end
 end
diff --git a/spec/lib/site_settings/validations_spec.rb b/spec/lib/site_settings/validations_spec.rb
new file mode 100644
index 00000000000..252099b4010
--- /dev/null
+++ b/spec/lib/site_settings/validations_spec.rb
@@ -0,0 +1,80 @@
+require 'rails_helper'
+require 'site_settings/validations'
+
+describe SiteSettings::Validations do
+  subject { Class.new.include(described_class).new }
+
+  context "s3 buckets reusage" do
+    let(:error_message) { I18n.t("errors.site_settings.s3_bucket_reused") }
+
+    shared_examples "s3 bucket validation" do
+      def change_bucket_value(value)
+        SiteSetting.public_send("#{other_setting_name}=", value)
+      end
+
+      it "shouldn't raise an error when both buckets are blank" do
+        change_bucket_value("")
+        expect { validate("") }.to_not raise_error
+      end
+
+      it "shouldn't raise an error when only one bucket is set" do
+        change_bucket_value("")
+        expect { validate("my-awesome-bucket") }.to_not raise_error
+      end
+
+      it "shouldn't raise an error when both buckets are equal, but use a different path" do
+        change_bucket_value("my-awesome-bucket/foo")
+        expect { validate("my-awesome-bucket/bar") }.to_not raise_error
+      end
+
+      it "should raise an error when both buckets are equal" do
+        change_bucket_value("my-awesome-bucket")
+        expect { validate("my-awesome-bucket") }.to raise_error(Discourse::InvalidParameters, error_message)
+      end
+
+      it "should raise an error when both buckets are equal except for a trailing slash" do
+        change_bucket_value("my-awesome-bucket/")
+        expect { validate("my-awesome-bucket") }.to raise_error(Discourse::InvalidParameters, error_message)
+
+        change_bucket_value("my-awesome-bucket")
+        expect { validate("my-awesome-bucket/") }.to raise_error(Discourse::InvalidParameters, error_message)
+      end
+    end
+
+    describe "#validate_s3_backup_bucket" do
+      let(:other_setting_name) { "s3_upload_bucket" }
+
+      def validate(new_value)
+        subject.validate_s3_backup_bucket(new_value)
+      end
+
+      it_behaves_like "s3 bucket validation"
+
+      it "shouldn't raise an error when the 's3_backup_bucket' is a subdirectory of 's3_upload_bucket'" do
+        SiteSetting.s3_upload_bucket = "my-awesome-bucket"
+        expect { validate("my-awesome-bucket/backups") }.to_not raise_error
+
+        SiteSetting.s3_upload_bucket = "my-awesome-bucket/foo"
+        expect { validate("my-awesome-bucket/foo/backups") }.to_not raise_error
+      end
+    end
+
+    describe "#validate_s3_upload_bucket" do
+      let(:other_setting_name) { "s3_backup_bucket" }
+
+      def validate(new_value)
+        subject.validate_s3_upload_bucket(new_value)
+      end
+
+      it_behaves_like "s3 bucket validation"
+
+      it "should raise an error when the 's3_upload_bucket' is a subdirectory of 's3_backup_bucket'" do
+        SiteSetting.s3_backup_bucket = "my-awesome-bucket"
+        expect { validate("my-awesome-bucket/uploads") }.to raise_error(Discourse::InvalidParameters, error_message)
+
+        SiteSetting.s3_backup_bucket = "my-awesome-bucket/foo"
+        expect { validate("my-awesome-bucket/foo/uploads") }.to raise_error(Discourse::InvalidParameters, error_message)
+      end
+    end
+  end
+end