diff --git a/application/forms/AddNodeForm.php b/application/forms/AddNodeForm.php
index 1d87305..6bfe392 100644
--- a/application/forms/AddNodeForm.php
+++ b/application/forms/AddNodeForm.php
@@ -117,6 +117,7 @@ class AddNodeForm extends QuickForm
                 '&' => $this->translate('AND'),
                 '|' => $this->translate('OR'),
                 '!' => $this->translate('NOT'),
+                '%' => $this->translate('DEGRADED'),
                 '1' => $this->translate('MIN 1'),
                 '2' => $this->translate('MIN 2'),
                 '3' => $this->translate('MIN 3'),
diff --git a/application/forms/EditNodeForm.php b/application/forms/EditNodeForm.php
index 588c6de..e97ae59 100644
--- a/application/forms/EditNodeForm.php
+++ b/application/forms/EditNodeForm.php
@@ -114,6 +114,7 @@ class EditNodeForm extends QuickForm
                 '&' => $this->translate('AND'),
                 '|' => $this->translate('OR'),
                 '!' => $this->translate('NOT'),
+                '%' => $this->translate('DEGRADED'),
                 '1' => $this->translate('MIN 1'),
                 '2' => $this->translate('MIN 2'),
                 '3' => $this->translate('MIN 3'),
diff --git a/application/forms/ProcessForm.php b/application/forms/ProcessForm.php
index 4cc3bcf..0e0b853 100644
--- a/application/forms/ProcessForm.php
+++ b/application/forms/ProcessForm.php
@@ -61,6 +61,7 @@ class ProcessForm extends QuickForm
                 '&' => $this->translate('AND'),
                 '|' => $this->translate('OR'),
                 '!' => $this->translate('NOT'),
+                '%' => $this->translate('DEGRADED'),
                 '1' => $this->translate('MIN 1'),
                 '2' => $this->translate('MIN 2'),
                 '3' => $this->translate('MIN 3'),
diff --git a/doc/09-Operators.md b/doc/09-Operators.md
index 53613f2..58db97c 100644
--- a/doc/09-Operators.md
+++ b/doc/09-Operators.md
@@ -17,6 +17,15 @@ The `OR` operator selects the **BEST** state of its child nodes:
 
 ![Or Operator #2](screenshot/09_operators/0903_or-operator-without-ok.png)
 
+## DEGRADED <a id="deg-operator">
+
+The `DEGRADED` operator behaves like an `AND`, but if the resulting
+state is **CRITICAL** it transforms it into a **WARNING**.
+Refer to the table below for the case-by-case
+analysis of the statuses.
+
+![Degraded Operator](screenshot/09_operators/0905_deg-operator.jpg)
+
 ## MIN n <a id="min-operator">
 
 The `MIN` operator selects the **WORST** state out of the **BEST n** child node states:
diff --git a/doc/screenshot/09_operators/0905_deg-operator.jpg b/doc/screenshot/09_operators/0905_deg-operator.jpg
new file mode 100644
index 0000000..9dc05a3
Binary files /dev/null and b/doc/screenshot/09_operators/0905_deg-operator.jpg differ
diff --git a/library/Businessprocess/BpNode.php b/library/Businessprocess/BpNode.php
index 58a7c11..6944f09 100644
--- a/library/Businessprocess/BpNode.php
+++ b/library/Businessprocess/BpNode.php
@@ -11,6 +11,7 @@ class BpNode extends Node
     const OP_AND = '&';
     const OP_OR  = '|';
     const OP_NOT  = '!';
+    const OP_DEGRADED  = '%';
 
     protected $operator = '&';
     protected $url;
@@ -289,6 +290,7 @@ class BpNode extends Node
             case self::OP_AND:
             case self::OP_OR:
             case self::OP_NOT:
+            case self::OP_DEGRADED:
                 return;
             default:
                 if (is_numeric($operator)) {
@@ -460,6 +462,15 @@ class BpNode extends Node
             case self::OP_OR:
                 $sort_state = min($sort_states);
                 break;
+            case self::OP_DEGRADED:
+                $maxState = max($sort_states);
+                $flags = $maxState & 0xf;
+
+                $maxIcingaState = $this->sortStateTostate($maxState);
+                $warningState = ($this->stateToSortState(self::ICINGA_WARNING) << self::SHIFT_FLAGS) + $flags;
+
+                $sort_state = ($maxIcingaState === self::ICINGA_CRITICAL) ? $warningState : $maxState;
+                break;
             default:
                 // MIN:
                 $sort_state = 3 << self::SHIFT_FLAGS;
@@ -624,6 +635,9 @@ class BpNode extends Node
             case self::OP_NOT:
                 return 'NOT';
                 break;
+            case self::OP_DEGRADED:
+                return 'DEG';
+                break;
             default:
                 // MIN
                 $this->assertNumericOperator();
diff --git a/library/Businessprocess/Storage/LegacyConfigParser.php b/library/Businessprocess/Storage/LegacyConfigParser.php
index 4142731..17fc8a5 100644
--- a/library/Businessprocess/Storage/LegacyConfigParser.php
+++ b/library/Businessprocess/Storage/LegacyConfigParser.php
@@ -322,7 +322,7 @@ class LegacyConfigParser
         }
 
         $op = '&';
-        if (preg_match_all('~(?<!\\\\)([\|\+&\!])~', $value, $m)) {
+        if (preg_match_all('~(?<!\\\\)([\|\+&\!\%])~', $value, $m)) {
             $op = implode('', $m[1]);
             for ($i = 1; $i < strlen($op); $i++) {
                 if ($op[$i] !== $op[$i - 1]) {
@@ -351,7 +351,7 @@ class LegacyConfigParser
 
         $cmps = preg_split('~\s*(?<!\\\\)\\' . $op . '\s*~', $value, -1, PREG_SPLIT_NO_EMPTY);
         foreach ($cmps as $val) {
-            $val = preg_replace('~(\\\\([\|\+&\!]))~', '$2', $val);
+            $val = preg_replace('~(\\\\([\|\+&\!\%]))~', '$2', $val);
             if (strpos($val, ';') !== false) {
                 if ($bp->hasNode($val)) {
                     $node->addChild($bp->getNode($val));
diff --git a/library/Businessprocess/Storage/LegacyConfigRenderer.php b/library/Businessprocess/Storage/LegacyConfigRenderer.php
index ebe9589..7e2e0b2 100644
--- a/library/Businessprocess/Storage/LegacyConfigRenderer.php
+++ b/library/Businessprocess/Storage/LegacyConfigRenderer.php
@@ -186,7 +186,7 @@ class LegacyConfigRenderer
         $op = static::renderOperator($node);
         $children = $node->getChildNames();
         $str = implode(' ' . $op . ' ', array_map(function ($val) {
-            return preg_replace('~([\|\+&\!])~', '\\\\$1', $val);
+            return preg_replace('~([\|\+&\!\%])~', '\\\\$1', $val);
         }, $children));
 
         if ((count($children) < 2) && $op !== '&') {
diff --git a/test/php/library/Businessprocess/BpNodeTest.php b/test/php/library/Businessprocess/BpNodeTest.php
index c1f224b..c3da723 100644
--- a/test/php/library/Businessprocess/BpNodeTest.php
+++ b/test/php/library/Businessprocess/BpNodeTest.php
@@ -7,22 +7,20 @@ use Icinga\Module\Businessprocess\Test\BaseTestCase;
 
 class BpNodeTest extends BaseTestCase
 {
-    /**
-     * @expectedException \Icinga\Module\Businessprocess\Exception\NestingError
-     */
     public function testThrowsNestingErrorWhenCheckedForLoops()
     {
+        $this->expectException(\Icinga\Module\Businessprocess\Exception\NestingError::class);
+
         /** @var BpNode $bpNode */
         $bpNode = $this->makeLoop()->getNode('d');
         $bpNode->checkForLoops();
     }
 
-    /**
-     * @expectedExceptionMessage d -> a -> b -> c -> a
-     * @expectedException \Icinga\Module\Businessprocess\Exception\NestingError
-     */
     public function testNestingErrorReportsFullLoop()
     {
+        $this->expectException(\Icinga\Module\Businessprocess\Exception\NestingError::class);
+        $this->expectExceptionMessage('d -> a -> b -> c -> a');
+
         /** @var BpNode $bpNode */
         $bpNode = $this->makeLoop()->getNode('d');
         $bpNode->checkForLoops();
diff --git a/test/php/library/Businessprocess/HostNodeTest.php b/test/php/library/Businessprocess/HostNodeTest.php
index 9839959..ef4155d 100644
--- a/test/php/library/Businessprocess/HostNodeTest.php
+++ b/test/php/library/Businessprocess/HostNodeTest.php
@@ -41,11 +41,9 @@ class HostNodeTest extends BaseTestCase
         );
     }
 
-    /**
-     * @expectedException \Icinga\Exception\ProgrammingError
-     */
     public function testSettingAnInvalidStateFails()
     {
+        $this->expectException(\Icinga\Exception\ProgrammingError::class);
         $bp = new BpConfig();
         $host = $bp->createHost('localhost')->setState(98);
         $bp->createBp('p')->addChild($host)->getState();
diff --git a/test/php/library/Businessprocess/Operators/DegradedOperatorTest.php b/test/php/library/Businessprocess/Operators/DegradedOperatorTest.php
new file mode 100644
index 0000000..72ed5e5
--- /dev/null
+++ b/test/php/library/Businessprocess/Operators/DegradedOperatorTest.php
@@ -0,0 +1,159 @@
+<?php
+
+namespace Tests\Icinga\Module\Businessprocess\Operator;
+
+use Icinga\Module\Businessprocess\BpConfig;
+use Icinga\Module\Businessprocess\Test\BaseTestCase;
+use Icinga\Module\Businessprocess\Storage\LegacyStorage;
+
+class DegradedOperatorTest extends BaseTestCase
+{
+    public function testDegradedOperatorCanBeParsed()
+    {
+        $storage = new LegacyStorage($this->emptyConfigSection());
+        $expressions = [
+            'a = b;c',
+            'a = b;c % c;d % d;e',
+        ];
+
+        foreach ($expressions as $expression) {
+            $this->assertInstanceOf(
+                'Icinga\\Module\\Businessprocess\\BpConfig',
+                $storage->loadFromString('dummy', $expression)
+            );
+        }
+    }
+
+    public function testThreeTimesCriticalIsWarning()
+    {
+        $bp = $this->getBp();
+        $bp->setNodeState('b;c', 2);
+        $bp->setNodeState('c;d', 2);
+        $bp->setNodeState('d;e', 2);
+
+        $this->assertEquals(
+            'WARNING',
+            $bp->getNode('a')->getStateName()
+        );
+    }
+
+    public function testTwoTimesCriticalAndOkIsWarning()
+    {
+        $bp = $this->getBp();
+        $bp->setNodeState('b;c', 2);
+        $bp->setNodeState('c;d', 0);
+        $bp->setNodeState('d;e', 2);
+
+        $this->assertEquals(
+            'WARNING',
+            $bp->getNode('a')->getStateName()
+        );
+    }
+
+    public function testCriticalAndWarningAndOkIsWarning()
+    {
+        $bp = $this->getBp();
+        $bp->setNodeState('b;c', 2);
+        $bp->setNodeState('c;d', 1);
+        $bp->setNodeState('d;e', 0);
+
+        $this->assertEquals(
+            'WARNING',
+            $bp->getNode('a')->getStateName()
+        );
+    }
+
+    public function testUnknownAndWarningAndOkIsUnknown()
+    {
+        $bp = $this->getBp();
+        $bp->setNodeState('b;c', 0);
+        $bp->setNodeState('c;d', 1);
+        $bp->setNodeState('d;e', 3);
+
+        $this->assertEquals(
+            'UNKNOWN',
+            $bp->getNode('a')->getStateName()
+        );
+    }
+
+    public function testTwoTimesWarningAndOkIsWarning()
+    {
+        $bp = $this->getBp();
+        $bp->setNodeState('b;c', 0);
+        $bp->setNodeState('c;d', 1);
+        $bp->setNodeState('d;e', 1);
+
+        $this->assertEquals(
+            'WARNING',
+            $bp->getNode('a')->getStateName()
+        );
+    }
+
+    public function testUnknownAndWarningAndCriticalIsWarning()
+    {
+        $bp = $this->getBp();
+        $bp->setNodeState('b;c', 2);
+        $bp->setNodeState('c;d', 1);
+        $bp->setNodeState('d;e', 3);
+
+        $this->assertEquals(
+            'WARNING',
+            $bp->getNode('a')->getStateName()
+        );
+    }
+
+    public function testThreeTimesOkIsOk()
+    {
+        $bp = $this->getBp();
+        $bp->setNodeState('b;c', 0);
+        $bp->setNodeState('c;d', 0);
+        $bp->setNodeState('d;e', 0);
+
+        $this->assertEquals(
+            'OK',
+            $bp->getNode('a')->getStateName()
+        );
+    }
+
+    public function testSimpleDegOperationWorksCorrectly()
+    {
+        $bp = new BpConfig();
+        $bp->throwErrors();
+        $host = $bp->createHost('localhost')->setState(0);
+        $service = $bp->createService('localhost', 'ping')->setState(2);
+        $p = $bp->createBp('p');
+        $p->setOperator('%');
+        $p->addChild($host);
+        $p->addChild($service);
+
+        $this->assertEquals(
+            'UP',
+            $host->getStateName()
+        );
+
+        $this->assertEquals(
+            'CRITICAL',
+            $service->getStateName()
+        );
+
+        $this->assertEquals(
+            'WARNING',
+            $p->getStateName()
+        );
+    }
+
+    /**
+     * @return BpConfig
+     */
+    protected function getBp()
+    {
+        $storage = new LegacyStorage($this->emptyConfigSection());
+        $expression = 'a = b;c % c;d % d;e';
+        $bp = $storage->loadFromString('dummy', $expression);
+        $bp->createBp('b');
+        $bp->createBp('c');
+        $bp->createBp('d');
+
+        return $bp;
+    }
+}