diff --git a/README.md b/README.md
index 3f17721..48b2ba6 100644
--- a/README.md
+++ b/README.md
@@ -443,6 +443,28 @@ To do this, pass a lambda as the value for the custom fact. The lambda is passed
 add_custom_fact :root_home, lambda { |os,facts| "/tmp/#{facts['hostname']}" }
 ```
 
+#### Merge into existing facts
+
+You can also supply an optional input `:merge_facts` to the `add_custom_fact` method.
+
+This allows you to merge facts values into a fact, if the fact is already present in the facts hash as oppose to overwriting the fact value.
+
+```ruby
+add_custom_fact 'identity', { 'user' => "test_user" }, :merge_facts => true
+```
+
+Will result in a hash of the identity fact like the below:
+
+```ruby
+{
+  "gid"=>0,
+  "group"=>"root",
+  "privileged"=>true,
+  "uid"=>0,
+  "user"=>"test_user"
+}
+```
+
 ### Supplying Custom External Facts through FacterDB
 Rspec-puppet-facts uses a gem called facterdb that contains many fact sets of various combinations that are pre generated.  Rspec-puppet-facts queries
 facterdb to pull out a specific fact set to use when testing.
diff --git a/lib/rspec-puppet-facts.rb b/lib/rspec-puppet-facts.rb
index 2d9e1e4..225f9e4 100644
--- a/lib/rspec-puppet-facts.rb
+++ b/lib/rspec-puppet-facts.rb
@@ -229,10 +229,13 @@ def self.with_custom_facts(os, facts)
       next if fact[:options][:confine] && !fact[:options][:confine].include?(os)
       next if fact[:options][:exclude] && fact[:options][:exclude].include?(os)
 
-      if fact[:value].respond_to?(:call)
-        facts = facts.deep_merge!({name.to_sym => fact[:value].call(os, facts)})
+      key = name.to_sym
+      value = fact[:value].respond_to?(:call) ? fact[:value].call(os, facts) : fact[:value]
+      # if merge_facts passed, merge supplied facts into facts hash
+      if fact[:options][:merge_facts]
+        facts = facts.deep_merge!({key => value})
       else
-        facts = facts.deep_merge!({name.to_sym => fact[:value]})
+        facts[key] = value
       end
     end
 
diff --git a/spec/rspec_puppet_facts_spec.rb b/spec/rspec_puppet_facts_spec.rb
index 64dab39..734cea0 100644
--- a/spec/rspec_puppet_facts_spec.rb
+++ b/spec/rspec_puppet_facts_spec.rb
@@ -904,6 +904,22 @@
       expect(subject['redhat-7-x86_64'][:root_home]).to eq '/root'
     end
 
+    it 'deep merges fact and values' do
+      add_custom_fact 'identity', { 'user' => "test_user" }, :merge_facts => true
+      expect(subject['redhat-7-x86_64'][:identity]).to eq({
+        "gid"=>0,
+        "group"=>"root",
+        "privileged"=>true,
+        "uid"=>0,
+        "user"=>"test_user"
+        })
+    end
+
+    it 'overwrites fact and values' do
+      add_custom_fact 'identity', { 'user' => 'root' }
+      expect(subject['redhat-7-x86_64'][:identity]).to eq({ 'user' => 'root' })
+    end
+
     it 'confines a fact to a particular operating system' do
       add_custom_fact 'root_home', '/root', :confine => 'redhat-7-x86_64'
       expect(subject['redhat-7-x86_64'][:root_home]).to eq '/root'