diff --git a/src/Entity/Key.php b/src/Entity/Key.php
index 97a7077..af94afd 100644
--- a/src/Entity/Key.php
+++ b/src/Entity/Key.php
@@ -287,10 +287,27 @@ class Key extends ConfigEntityBase implements KeyInterface, EntityWithPluginColl
    * {@inheritdoc}
    */
   public function preSave(EntityStorageInterface $storage) {
-    // If the provider allows setting a key value and a value exists.
-    if ($this->getKeyProvider() instanceof KeyProviderSettableValueInterface && isset($this->keyValue)) {
-      // Set the key value using the key provider.
-      $this->getKeyProvider()->setKeyValue($this, $this->keyValue);
+    // If the key provider supports setting a key value.
+    if ($this->getKeyProvider() instanceof KeyProviderSettableValueInterface) {
+      // If a key value was defined.
+      if (isset($this->keyValue)) {
+        // Set the key value using the key provider.
+        $this->getKeyProvider()->setKeyValue($this, $this->keyValue);
+      }
+      // If a key value was not defined.
+      else {
+        // If the provider requires a key value, throw an exception.
+        if ($this->getKeyProvider()->getPluginDefinition()['key_value']['required']) {
+          throw new KeyValueNotSetException('The selected key provider requires a key value.');
+        }
+      }
+    }
+    // If the key provider does not support setting a value.
+    else {
+      // If a key value was defined, throw an exception.
+      if (isset($this->keyValue)) {
+        throw new KeyValueNotSetException('The selected key provider does not support setting a key value.');
+      }
     }
 
     parent::preSave($storage);