diff --git a/lib/data_update_scripts/20211115154021_nullify_invalid_tag_fields.rb b/lib/data_update_scripts/20211115154021_nullify_invalid_tag_fields.rb
new file mode 100644
index 000000000..ecc08dbef
--- /dev/null
+++ b/lib/data_update_scripts/20211115154021_nullify_invalid_tag_fields.rb
@@ -0,0 +1,34 @@
+module DataUpdateScripts
+  class NullifyInvalidTagFields
+    def run
+      Tag.where(bg_color_hex: "").or(Tag.where(text_color_hex: "")).find_each do |tag|
+        # presence here selects non-empty strings if set  (avoiding unsetting valid values)
+        # but nullifies empty tag colors
+        tag.update_columns(
+          bg_color_hex: tag.bg_color_hex.presence,
+          text_color_hex: tag.text_color_hex.presence,
+        )
+      end
+
+      # normalize empty string to nil (alias_for? behaved correctly already), this is just cleanup
+      Tag.where(alias_for: "").update(alias_for: nil)
+
+      Tag.where.not(alias_for: nil).find_each do |aliased_tag|
+        # this is expected to not do anything - based on this query in blazer giving 0 rows
+        # (there are 64 with aliases, all valid)
+
+        # SELECT tags.alias_for, t2.name FROM tags
+        # LEFT JOIN tags AS t2 ON tags.alias_for = t2.name
+        # WHERE tags.alias_for IS NOT NULL
+        # AND tags.alias_for != ''
+        # AND t2.name IS NULL;
+
+        aliased_tag.validate
+
+        if aliased_tag.errors.any? { |e| e.type == "alias_for must refer to an existing tag" }
+          aliased_tag.update_column(:alias_for, nil)
+        end
+      end
+    end
+  end
+end
diff --git a/spec/lib/data_update_scripts/nullify_invalid_tag_fields_spec.rb b/spec/lib/data_update_scripts/nullify_invalid_tag_fields_spec.rb
new file mode 100644
index 000000000..f28409c0c
--- /dev/null
+++ b/spec/lib/data_update_scripts/nullify_invalid_tag_fields_spec.rb
@@ -0,0 +1,53 @@
+require "rails_helper"
+require Rails.root.join(
+  "lib/data_update_scripts/20211115154021_nullify_invalid_tag_fields.rb",
+)
+
+describe DataUpdateScripts::NullifyInvalidTagFields do
+  let(:tag) { create(:tag) }
+
+  it "nullifies empty background color" do
+    tag.update_column(:bg_color_hex, "")
+
+    described_class.new.run
+
+    expect(tag.reload.bg_color_hex).to be_nil
+    expect(tag.valid?).to be true
+  end
+
+  it "nullifies empty text foreground color" do
+    tag.update_column(:text_color_hex, "")
+
+    described_class.new.run
+
+    expect(tag.reload.text_color_hex).to be_nil
+    expect(tag.valid?).to be true
+  end
+
+  it "nullifies when both colors empty" do
+    tag.update_columns(bg_color_hex: "", text_color_hex: "")
+
+    described_class.new.run
+
+    expect(tag.reload.text_color_hex).to be_nil
+    expect(tag.valid?).to be true
+  end
+
+  it "nullifies invalid alias_for values" do
+    tag.update_columns(alias_for: "this-is-not-a-tag-name")
+
+    described_class.new.run
+
+    expect(tag.reload.alias_for).to be_nil
+    expect(tag.valid?).to be true
+  end
+
+  it "nullifies empty string alias_for values" do
+    tag.update(alias_for: "")
+
+    described_class.new.run
+
+    expect(tag.reload.alias_for).to be_nil
+    expect(tag.valid?).to be true
+  end
+end