diff --git a/lib/vmpooler/pool_manager.rb b/lib/vmpooler/pool_manager.rb
index 55df2d9..be71a6c 100644
--- a/lib/vmpooler/pool_manager.rb
+++ b/lib/vmpooler/pool_manager.rb
@@ -710,21 +710,24 @@ module Vmpooler
       # INVENTORY
       inventory = {}
       begin
-        provider.vms_in_pool(pool['name']).each do |vm|
-          if !$redis.sismember('vmpooler__running__' + pool['name'], vm['name']) &&
-             !$redis.sismember('vmpooler__ready__' + pool['name'], vm['name']) &&
-             !$redis.sismember('vmpooler__pending__' + pool['name'], vm['name']) &&
-             !$redis.sismember('vmpooler__completed__' + pool['name'], vm['name']) &&
-             !$redis.sismember('vmpooler__discovered__' + pool['name'], vm['name']) &&
-             !$redis.sismember('vmpooler__migrating__' + pool['name'], vm['name'])
+        mutex = pool_mutex(pool['name'])
+        mutex.synchronize do
+          provider.vms_in_pool(pool['name']).each do |vm|
+            if !$redis.sismember('vmpooler__running__' + pool['name'], vm['name']) &&
+               !$redis.sismember('vmpooler__ready__' + pool['name'], vm['name']) &&
+               !$redis.sismember('vmpooler__pending__' + pool['name'], vm['name']) &&
+               !$redis.sismember('vmpooler__completed__' + pool['name'], vm['name']) &&
+               !$redis.sismember('vmpooler__discovered__' + pool['name'], vm['name']) &&
+               !$redis.sismember('vmpooler__migrating__' + pool['name'], vm['name'])
 
-            pool_check_response[:discovered_vms] += 1
-            $redis.sadd('vmpooler__discovered__' + pool['name'], vm['name'])
+              pool_check_response[:discovered_vms] += 1
+              $redis.sadd('vmpooler__discovered__' + pool['name'], vm['name'])
 
-            $logger.log('s', "[?] [#{pool['name']}] '#{vm['name']}' added to 'discovered' queue")
+              $logger.log('s', "[?] [#{pool['name']}] '#{vm['name']}' added to 'discovered' queue")
+            end
+
+            inventory[vm['name']] = 1
           end
-
-          inventory[vm['name']] = 1
         end
       rescue => err
         $logger.log('s', "[!] [#{pool['name']}] _check_pool failed with an error while inspecting inventory: #{err}")
diff --git a/spec/unit/pool_manager_spec.rb b/spec/unit/pool_manager_spec.rb
index 7e14928..579917a 100644
--- a/spec/unit/pool_manager_spec.rb
+++ b/spec/unit/pool_manager_spec.rb
@@ -2693,6 +2693,7 @@ EOT
     let(:pool_object) { config[:pools][0] }
     let(:new_vm) { 'newvm'}
     let(:pool_name) { pool_object['name'] }
+    let(:mutex) { Mutex.new }
 
     before do
       expect(subject).not_to be_nil
@@ -2798,6 +2799,27 @@ EOT
           end
         end
       end
+
+      it 'should get the pool mutex' do
+        expect(subject).to receive(:pool_mutex).and_return(mutex).at_least(:once)
+
+        subject._check_pool(pool_object,provider)
+      end
+
+      it 'should run synchronize' do
+        expect(subject).to receive(:pool_mutex).and_return(mutex).at_least(:once)
+        expect(mutex).to receive(:synchronize).at_least(:once)
+
+        subject._check_pool(pool_object,provider)
+      end
+
+      it 'should yield when locked' do
+        expect(subject).to receive(:pool_mutex).and_return(mutex).at_least(:once)
+        mutex.lock
+        expect(mutex).to receive(:synchronize).and_yield
+
+        subject._check_pool(pool_object,provider)
+      end
     end
 
     # RUNNING