diff --git a/lib/vmpooler.rb b/lib/vmpooler.rb
index 8b86fdb..c68e4ef 100644
--- a/lib/vmpooler.rb
+++ b/lib/vmpooler.rb
@@ -3,6 +3,7 @@
 module Vmpooler
   require 'concurrent'
   require 'date'
+  require 'deep_merge'
   require 'json'
   require 'net/ldap'
   require 'open-uri'
@@ -42,7 +43,7 @@ module Vmpooler
         extra_configs = parsed_config[:config]['extra_config'].split(',')
         extra_configs.each do |config|
           extra_config = YAML.load_file(config)
-          parsed_config.merge!(extra_config)
+          parsed_config.deep_merge(extra_config)
         end
       end
     end
diff --git a/spec/fixtures/extra_config1.yaml b/spec/fixtures/extra_config1.yaml
new file mode 100644
index 0000000..d19523c
--- /dev/null
+++ b/spec/fixtures/extra_config1.yaml
@@ -0,0 +1,4 @@
+---
+:providers:
+  :alice:
+    foo: "foo"
\ No newline at end of file
diff --git a/spec/fixtures/extra_config2.yaml b/spec/fixtures/extra_config2.yaml
new file mode 100644
index 0000000..e9f30d8
--- /dev/null
+++ b/spec/fixtures/extra_config2.yaml
@@ -0,0 +1,11 @@
+---
+:providers:
+  :bob:
+    foo: "foo_bob"
+    bar: "bar"
+
+:pools:
+  - name: 'pool05'
+    size: 5
+    provider: dummy
+    ready_ttl: 5
\ No newline at end of file
diff --git a/spec/unit/vmpooler_spec.rb b/spec/unit/vmpooler_spec.rb
index 19aed91..84d43ed 100644
--- a/spec/unit/vmpooler_spec.rb
+++ b/spec/unit/vmpooler_spec.rb
@@ -45,10 +45,30 @@ describe 'Vmpooler' do
     end
 
     context 'when config file is set' do
-      it 'should use the file' do
+      before(:each) do
         ENV['VMPOOLER_CONFIG_FILE'] = config_file
+      end
+      it 'should use the file' do
         expect(Vmpooler.config[:pools]).to eq(config[:pools])
       end
+      it 'merges one extra file, results in two providers' do
+        ENV['EXTRA_CONFIG'] = File.join(fixtures_dir, 'extra_config1.yaml')
+        expect(Vmpooler.config[:providers].keys).to include(:dummy)
+        expect(Vmpooler.config[:providers].keys).to include(:alice)
+      end
+      it 'merges two extra file, results in three providers and an extra pool' do
+        extra1 = File.join(fixtures_dir, 'extra_config1.yaml')
+        extra2 = File.join(fixtures_dir, 'extra_config2.yaml')
+        ENV['EXTRA_CONFIG'] = "#{extra1},#{extra2}"
+        expect(Vmpooler.config[:providers].keys).to include(:dummy)
+        expect(Vmpooler.config[:providers].keys).to include(:alice)
+        expect(Vmpooler.config[:providers].keys).to include(:bob)
+        merged_pools = [{"name"=>"pool03", "provider"=>"dummy", "ready_ttl"=>5, "size"=>5},
+                        {"name"=>"pool04", "provider"=>"dummy", "ready_ttl"=>5, "size"=>5},
+                        {"name"=>"pool05", "provider"=>"dummy", "ready_ttl"=>5, "size"=>5}]
+        expect(Vmpooler.config[:pools]).to eq(merged_pools)
+        expect(Vmpooler.config[:config]).not_to be_nil #merge does not deleted existing keys
+      end
     end
   end
 end
diff --git a/vmpooler.gemspec b/vmpooler.gemspec
index 1f3299e..144ae0b 100644
--- a/vmpooler.gemspec
+++ b/vmpooler.gemspec
@@ -19,6 +19,7 @@ Gem::Specification.new do |s|
   s.require_paths = ["lib"]
   s.add_dependency 'concurrent-ruby', '~> 1.1'
   s.add_dependency 'connection_pool', '~> 2.2'
+  s.add_dependency 'deep_merge', '~> 1.2'
   s.add_dependency 'net-ldap', '~> 0.16'
   s.add_dependency 'nokogiri', '~> 1.10'
   s.add_dependency 'opentelemetry-exporter-jaeger', '= 0.20.1'