diff --git a/lib/rackstash/fields/abstract_collection.rb b/lib/rackstash/fields/abstract_collection.rb
index 5dfa130..dfa4100 100644
--- a/lib/rackstash/fields/abstract_collection.rb
+++ b/lib/rackstash/fields/abstract_collection.rb
@@ -11,9 +11,13 @@ require 'uri'
 
 require 'concurrent'
 
+require 'rackstash/helpers'
+
 module Rackstash
   module Fields
     class AbstractCollection
+      include Rackstash::Helpers::UTF8
+
       # Equality -- Two collections are equal if they are of exactly the same
       # class and contain the same raw data according to `Object#==`.
       #
@@ -87,22 +91,6 @@ module Rackstash
         end
       end
 
-      # Encode the given String in UTF-8. If the given `str` is already
-      # correctly encoded and frozen, we just return it unchanged. In all other
-      # cases we return a UTF-8 encoded and frozen copy of the string.
-      #
-      # @param str [String, #to_s]
-      # @return [String]
-      def utf8_encode(str)
-        if str.instance_of?(String) && str.encoding == Encoding::UTF_8 && str.valid_encoding?
-          str.frozen? ? str : str.dup.freeze
-        else
-          str = str.to_s
-          str = str.encode(Encoding::UTF_8, invalid: :replace, undef: :replace)
-          str.freeze
-        end
-      end
-
       def resolve_value(value, scope: nil)
         return value unless value.is_a?(Proc)
         scope.nil? ? value.call : scope.instance_exec(&value)
@@ -189,7 +177,7 @@ module Rackstash
           return normalize(value, scope: scope, wrap: wrap)
         end
 
-        utf8_encode(value.inspect)
+        utf8_encode(value.inspect.freeze)
       end
     end
   end
diff --git a/lib/rackstash/fields/tags.rb b/lib/rackstash/fields/tags.rb
index 3b76623..3fdc5b0 100644
--- a/lib/rackstash/fields/tags.rb
+++ b/lib/rackstash/fields/tags.rb
@@ -76,7 +76,7 @@ module Rackstash
           value.flatten!
           value
         else
-          utf8_encode(value).strip
+          utf8_encode(value).strip.freeze
         end
       end
     end
diff --git a/lib/rackstash/helpers.rb b/lib/rackstash/helpers.rb
new file mode 100644
index 0000000..e403eef
--- /dev/null
+++ b/lib/rackstash/helpers.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+# Copyright 2017 Holger Just
+#
+# This software may be modified and distributed under the terms
+# of the MIT license. See the LICENSE.txt file for details.
+
+module Rackstash
+  # Some utility function which are used throughout Rackstash.
+  module Helpers
+  end
+end
+
+require 'rackstash/helpers/utf8'
diff --git a/lib/rackstash/helpers/utf8.rb b/lib/rackstash/helpers/utf8.rb
new file mode 100644
index 0000000..6665216
--- /dev/null
+++ b/lib/rackstash/helpers/utf8.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+# Copyright 2017 Holger Just
+#
+# This software may be modified and distributed under the terms
+# of the MIT license. See the LICENSE.txt file for details.
+
+module Rackstash
+  module Helpers
+    # Provide helper functions to help with UTF8 handling of Strings.
+    module UTF8
+      protected
+
+      # Encode the given String in UTF-8. If the given `str` is already
+      # correctly encoded and frozen, we just return it unchanged. In all other
+      # cases we return a UTF-8 encoded and frozen copy of the string.
+      #
+      # @param str [String, #to_s]
+      # @return [String]
+      def utf8_encode(str)
+        if str.instance_of?(String) && str.encoding == Encoding::UTF_8 && str.valid_encoding?
+          str.frozen? ? str : str.dup.freeze
+        else
+          str = str.to_s
+          str = str.encode(Encoding::UTF_8, invalid: :replace, undef: :replace)
+          str.freeze
+        end
+      end
+    end
+  end
+end
diff --git a/spec/rackstash/fields/abstract_collection_spec.rb b/spec/rackstash/fields/abstract_collection_spec.rb
index 5f3b8fc..7a8f017 100644
--- a/spec/rackstash/fields/abstract_collection_spec.rb
+++ b/spec/rackstash/fields/abstract_collection_spec.rb
@@ -116,47 +116,14 @@ describe Rackstash::Fields::AbstractCollection do
   end
 
   describe '#normalize' do
-    describe 'with String' do
-      it 'transforms encoding to UTF-8' do
-        utf8_str = 'Dönerstraße'
-        latin_str = utf8_str.encode(Encoding::ISO8859_9)
-        expect(latin_str.encoding).to eql Encoding::ISO8859_9
+    it 'encodes Strings to UTF-8' do
+      utf8_str = 'Dönerstraße'
+      latin_str = utf8_str.encode(Encoding::ISO8859_9)
+      expect(latin_str.encoding).to eql Encoding::ISO8859_9
 
-        expect(normalize(latin_str)).to eql utf8_str
-        expect(normalize(latin_str).encoding).to eql Encoding::UTF_8
-        expect(normalize(latin_str)).to be_frozen
-      end
-
-      it 'replaces invalid characters in correctly encoded strings' do
-        binary = Digest::SHA256.digest('string')
-
-        expect(normalize(binary)).to include '�'
-        expect(normalize(binary).encoding).to eql Encoding::UTF_8
-        expect(normalize(binary)).to be_frozen
-      end
-
-      it 'replaces invalid characters in incorrectly encoded strings' do
-        strange = Digest::SHA256.digest('string').force_encoding(Encoding::UTF_8)
-
-        expect(normalize(strange)).to include '�'
-        expect(normalize(strange).encoding).to eql Encoding::UTF_8
-        expect(normalize(strange)).to be_frozen
-      end
-
-      it 'dups and freezes valid strings' do
-        valid = String.new('Dönerstraße')
-        expect(valid).to_not be_frozen
-
-        expect(normalize(valid)).to eql(valid)
-        # Not object-equal since the string was dup'ed
-        expect(normalize(valid)).not_to equal valid
-        expect(normalize(valid)).to be_frozen
-      end
-
-      it 'does not alter valid frozen strings' do
-        valid = 'Dönerstraße'.freeze
-        expect(normalize(valid)).to equal(valid)
-      end
+      expect(normalize(latin_str)).to eql utf8_str
+      expect(normalize(latin_str).encoding).to eql Encoding::UTF_8
+      expect(normalize(latin_str)).to be_frozen
     end
 
     it 'transforms Symbol to String' do
diff --git a/spec/rackstash/helpers/utf8_spec.rb b/spec/rackstash/helpers/utf8_spec.rb
new file mode 100644
index 0000000..460729b
--- /dev/null
+++ b/spec/rackstash/helpers/utf8_spec.rb
@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+# Copyright 2017 Holger Just
+#
+# This software may be modified and distributed under the terms
+# of the MIT license. See the LICENSE.txt file for details.
+
+require 'spec_helper'
+
+require 'rackstash/helpers/utf8'
+
+describe Rackstash::Helpers::UTF8 do
+  it 'only defines protected methods' do
+    expect(described_class.public_instance_methods(false)).to be_empty
+  end
+
+  describe '#utf8_encode' do
+    def utf8_encode(*args)
+      Object.new.extend(described_class).send(:utf8_encode, *args)
+    end
+
+    it 'transforms encoding to UTF-8' do
+      utf8_str = 'Dönerstraße'
+      latin_str = utf8_str.encode(Encoding::ISO8859_9)
+      expect(latin_str.encoding).to eql Encoding::ISO8859_9
+
+      expect(utf8_encode(latin_str)).to eql utf8_str
+      expect(utf8_encode(latin_str).encoding).to eql Encoding::UTF_8
+      expect(utf8_encode(latin_str)).to be_frozen
+    end
+
+    it 'replaces invalid characters in correctly encoded strings' do
+      binary = Digest::SHA256.digest('string')
+
+      expect(utf8_encode(binary)).to include '�'
+      expect(utf8_encode(binary).encoding).to eql Encoding::UTF_8
+      expect(utf8_encode(binary)).to be_frozen
+    end
+
+    it 'replaces invalid characters in incorrectly encoded strings' do
+      strange = Digest::SHA256.digest('string').force_encoding(Encoding::UTF_8)
+
+      expect(utf8_encode(strange)).to include '�'
+      expect(utf8_encode(strange).encoding).to eql Encoding::UTF_8
+      expect(utf8_encode(strange)).to be_frozen
+    end
+
+    it 'dups and freezes valid strings' do
+      valid = String.new('Dönerstraße')
+      expect(valid).to_not be_frozen
+
+      expect(utf8_encode(valid)).to eql(valid)
+      # Not object-equal since the string was dup'ed
+      expect(utf8_encode(valid)).not_to equal valid
+      expect(utf8_encode(valid)).to be_frozen
+    end
+
+    it 'does not alter valid frozen strings' do
+      valid = 'Dönerstraße'.freeze
+      expect(utf8_encode(valid)).to equal(valid)
+    end
+  end
+end