diff --git a/Model/ModelRegistry.php b/Model/ModelRegistry.php
index db346fb87..7631d0bd9 100644
--- a/Model/ModelRegistry.php
+++ b/Model/ModelRegistry.php
@@ -100,7 +100,11 @@ public function registerSchemas(): void
                 }
 
                 if (null === $schema) {
-                    throw new \LogicException(sprintf('Schema of type "%s" can\'t be generated, no describer supports it.', $this->typeToString($model->getType())));
+                    $errorMessage = sprintf('Schema of type "%s" can\'t be generated, no describer supports it.', $this->typeToString($model->getType()));
+                    if (Type::BUILTIN_TYPE_OBJECT === $model->getType()->getBuiltinType() && !class_exists($className = $model->getType()->getClassName())) {
+                        $errorMessage .= sprintf(' Class "\\%s" does not exist, did you forget a use statement, or typed it wrong?', $className);
+                    }
+                    throw new \LogicException($errorMessage);
                 }
             }
         }
@@ -174,7 +178,7 @@ private function getTypeShortName(Type $type): string
     private function typeToString(Type $type): string
     {
         if (Type::BUILTIN_TYPE_OBJECT === $type->getBuiltinType()) {
-            return $type->getClassName();
+            return '\\'.$type->getClassName();
         } elseif ($type->isCollection()) {
             if (null !== $collectionType = $this->getCollectionValueType($type)) {
                 return $this->typeToString($collectionType).'[]';
diff --git a/Tests/Model/ModelRegistryTest.php b/Tests/Model/ModelRegistryTest.php
index ef7fd853e..fdbbc3600 100644
--- a/Tests/Model/ModelRegistryTest.php
+++ b/Tests/Model/ModelRegistryTest.php
@@ -234,7 +234,20 @@ public function unsupportedTypesProvider()
     {
         return [
             [new Type(Type::BUILTIN_TYPE_ARRAY, false, null, true), 'mixed[]'],
-            [new Type(Type::BUILTIN_TYPE_OBJECT, false, self::class), self::class],
+            [new Type(Type::BUILTIN_TYPE_OBJECT, false, self::class), '\\'.self::class],
         ];
     }
+
+    public function testUnsupportedTypeExceptionWithNonExistentClass()
+    {
+        $className = DoesNotExist::class;
+        $type = new Type(Type::BUILTIN_TYPE_OBJECT, false, $className);
+
+        $this->expectException('\LogicException');
+        $this->expectExceptionMessage(sprintf('Schema of type "\%s" can\'t be generated, no describer supports it. Class "\Nelmio\ApiDocBundle\Tests\Model\DoesNotExist" does not exist, did you forget a use statement, or typed it wrong?', $className));
+
+        $registry = new ModelRegistry([], new OA\OpenApi([]));
+        $registry->register(new Model($type));
+        $registry->registerSchemas();
+    }
 }