diff --git a/lib/metrics/tags.rb b/lib/metrics/tags.rb
index 60a3b83..f5f462b 100644
--- a/lib/metrics/tags.rb
+++ b/lib/metrics/tags.rb
@@ -5,11 +5,15 @@
 
 module Metrics
 	module Tags
+		INVALID_TAG_CHARACTERS = /[^a-z0-9\-_\.:\\]/i
+		
 		def self.normalize(tags)
 			return nil unless tags&.any?
 			
 			if tags.is_a?(Hash)
-				tags = tags.map{|key, value| "#{key}:#{value}"}
+				tags = tags.map do |key, value|
+					"#{key}:#{value}".gsub(INVALID_TAG_CHARACTERS, "_").slice(0, 127)
+				end
 			end
 			
 			return Array(tags)
diff --git a/test/metrics/tags.rb b/test/metrics/tags.rb
new file mode 100644
index 0000000..5f25faa
--- /dev/null
+++ b/test/metrics/tags.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2024, by Samuel Williams.
+
+require "metrics/tags"
+
+describe Metrics::Tags do
+	it "can normalize an ipv6 address" do
+		tags = subject.normalize({"ip" => "[::1]"})
+		
+		expect(tags).to be == ["ip:_::1_"]
+	end
+end