diff --git a/lib/rackstash/fields/tags.rb b/lib/rackstash/fields/tags.rb
index 0a57d81..8bafe84 100644
--- a/lib/rackstash/fields/tags.rb
+++ b/lib/rackstash/fields/tags.rb
@@ -41,7 +41,7 @@ module Rackstash
       end
 
       def merge!(tags, scope: nil)
-        @raw.merge normalize_tags(tags)
+        @raw.merge normalize_tags(tags, scope: scope)
         self
       end
 
@@ -61,11 +61,11 @@ module Rackstash
         if value.is_a?(self.class)
           value.to_a
         elsif value.is_a?(Set)
-          value = value.map { |tag| normalize_tags(tag) }
+          value = value.map { |tag| normalize_tags(tag, scope: scope) }
           value.flatten!
           value
         elsif value.respond_to?(:to_ary)
-          value = value.to_ary.map { |tag| normalize_tags(tag) }
+          value = value.to_ary.map { |tag| normalize_tags(tag, scope: scope) }
           value.flatten!
           value
         else
diff --git a/spec/rackstash/fields/tags_spec.rb b/spec/rackstash/fields/tags_spec.rb
index 904475b..67c7900 100644
--- a/spec/rackstash/fields/tags_spec.rb
+++ b/spec/rackstash/fields/tags_spec.rb
@@ -11,7 +11,7 @@ describe Rackstash::Fields::Tags do
   let(:tags) { Rackstash::Fields::Tags.new }
 
   describe '#<<' do
-    it 'calls merge!' do
+    it 'adds a single tag' do
       tags << 'tag'
       expect(tags.tagged?('tag')).to be true
     end
@@ -94,7 +94,10 @@ describe Rackstash::Fields::Tags do
 
     it 'resolves procs' do
       tags.merge! [-> { 123 }]
-      expect(tags.tagged?('123')).to be true
+      expect(tags.to_a).to eql ['123']
+
+      tags.merge! [-> { self }], scope: :foo
+      expect(tags.to_a).to eql ['123', 'foo']
     end
 
     it 'flattens arguments' do