diff --git a/src/Generator/ClientGenerator.php b/src/Generator/ClientGenerator.php
index 517715f..f2c82d9 100644
--- a/src/Generator/ClientGenerator.php
+++ b/src/Generator/ClientGenerator.php
@@ -34,7 +34,8 @@ class ClientGenerator
 {
     private SchemaToClass $classBuilder;
     private WriterInterface $writer;
-    private SchemaReferenceLookup $referenceLookup;
+    private SchemaReferenceLookup $requestReferenceLookup;
+    private SchemaReferenceLookup $responseReferenceLookup;
 
     public function __construct(
         private readonly Context              $context,
@@ -45,7 +46,10 @@ public function __construct(
         $output                = new ConsoleOutput();
         $this->writer          = new FileWriter($output);
         $this->classBuilder    = $s2c->build($this->writer, $output);
-        $this->referenceLookup = new SchemaReferenceLookup($this->context);
+        // Unknown enum values from the API must not break deserialization of responses; in
+        // requests they are still an error on the caller's side and fail before being sent.
+        $this->requestReferenceLookup  = new SchemaReferenceLookup($this->context);
+        $this->responseReferenceLookup = new SchemaReferenceLookup($this->context, tolerantEnums: true);
     }
 
     /**
@@ -254,7 +258,7 @@ private function buildOperationRequestClass(string $namespace, string $methodNam
         $req = $req->withAdditionalMethod($buildUrlMethod);
         $req = $req->withAdditionalMethod($buildRequestOptionsMethod);
         $req = $req->withAdditionalMethod($withHeaderMethod);
-        $req = $req->withReferenceLookup($this->referenceLookup);
+        $req = $req->withReferenceLookup($this->requestReferenceLookup);
 
         $this->classBuilder->schemaToClass($req);
         return $paramClassNameFQ;
@@ -350,7 +354,7 @@ private function buildOperationMethod(string $namespace, string $tag, string $pa
             ];
 
             $req = new GeneratorRequest($envelopedResponseSchema, new ValidatedSpecificationFilesItem($responseClassNamespace, $responseClassName, $outputDir), $this->generatorOpts)
-                ->withReferenceLookup($this->referenceLookup)
+                ->withReferenceLookup($this->responseReferenceLookup)
                 ->withAdditionalMethod($factoryMethod)
                 ->withAdditionalMethod($getResponseMethod)
                 ->withAdditionalProperty($httpResponseProperty)
diff --git a/src/Generator/ComponentGenerator.php b/src/Generator/ComponentGenerator.php
index 67b34b0..d418523 100644
--- a/src/Generator/ComponentGenerator.php
+++ b/src/Generator/ComponentGenerator.php
@@ -68,6 +68,11 @@ public function generate(string $baseNamespace, array $component, string $compon
             return;
         }
 
+        // Add a fallback case for values added to the API after generation; see TolerantReferencedTypeEnum.
+        if (isset($component["enum"]) && ($component["type"] ?? null) === "string") {
+            $component["enum"][] = TolerantReferencedTypeEnum::FallbackValue;
+        }
+
         $className = $baseNamespace . "\\" . static::componentNameToClassName($componentName);
         $namespace = substr($className, 0, strrpos($className, "\\"));
         $classNameWithoutNamespace = substr($className, strrpos($className, "\\") + 1);
@@ -81,7 +86,7 @@ public function generate(string $baseNamespace, array $component, string $compon
             ->withNewValidatorClassExpr("new \Mittwald\ApiClient\Validator\Validator()");
 
         $request = new GeneratorRequest($component, $spec, $opts);
-        $request = $request->withReferenceLookup(new SchemaReferenceLookup($this->context));
+        $request = $request->withReferenceLookup(new SchemaReferenceLookup($this->context, tolerantEnums: true));
         $request = $request->withHook(new class($component, $componentName) implements ClassCreatedHook {
             function __construct(private readonly array $component, private readonly string $componentName) {}
 
diff --git a/src/Generator/SchemaReferenceLookup.php b/src/Generator/SchemaReferenceLookup.php
index 697bdc3..848f241 100644
--- a/src/Generator/SchemaReferenceLookup.php
+++ b/src/Generator/SchemaReferenceLookup.php
@@ -9,7 +9,10 @@
 
 class SchemaReferenceLookup implements ReferenceLookup
 {
-    public function __construct(private readonly Context $context)
+    public function __construct(
+        private readonly Context $context,
+        private readonly bool    $tolerantEnums = false,
+    )
     {
     }
 
@@ -79,12 +82,21 @@ public function lookupSchema(string $reference): array
         return $this->context->schema["components"][$componentType][$name];
     }
 
+    private function buildEnumReference(string $fqcn, array $schema): ReferencedTypeEnum
+    {
+        if ($this->tolerantEnums && ($schema["type"] ?? null) === "string") {
+            return new TolerantReferencedTypeEnum($fqcn);
+        }
+
+        return new ReferencedTypeEnum($fqcn);
+    }
+
     private function buildTypeReference(string $fqcn, array $schema): ReferencedType
     {
         return match (true) {
-            isset($schema["enum"]) => new ReferencedTypeEnum($fqcn),
+            isset($schema["enum"]) => $this->buildEnumReference($fqcn, $schema),
             isset($schema["items"]["\$ref"]) => new ReferencedTypeList($this->lookupReference($schema["items"]["\$ref"])),
-            isset($schema["items"]["enum"]) => new ReferencedTypeList(new ReferencedTypeEnum($fqcn . "Item")),
+            isset($schema["items"]["enum"]) => new ReferencedTypeList($this->buildEnumReference($fqcn . "Item", $schema["items"])),
             isset($schema["items"]) => new ReferencedTypeList($this->buildTypeReference($fqcn . "Item", $schema["items"])),
             isset($schema["type"]) && $schema["type"] === "string" => new ReferencedString(),
             isset($schema["oneOf"]) => $this->buildUnionType($fqcn, $schema["oneOf"]),
diff --git a/src/Generator/TolerantReferencedTypeEnum.php b/src/Generator/TolerantReferencedTypeEnum.php
new file mode 100644
index 0000000..c7520d5
--- /dev/null
+++ b/src/Generator/TolerantReferencedTypeEnum.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace Mittwald\ApiToolsPHP\Generator;
+
+use Helmich\Schema2Class\Generator\GeneratorRequest;
+use Helmich\Schema2Class\Generator\ReferencedTypeEnum;
+use Helmich\Schema2Class\Generator\SchemaToEnum;
+
+/**
+ * A referenced enum that tolerates values the generated enum does not know, by mapping them to a
+ * fallback case instead of raising a ValueError. This keeps released clients working when new
+ * values are added to an enum in the API schema. The fallback case is added to the generated enums
+ * by appending {@see self::FallbackValue} to their schema (see ComponentGenerator).
+ */
+readonly class TolerantReferencedTypeEnum extends ReferencedTypeEnum
+{
+    public const FallbackValue = "__unknown__";
+
+    public function inputMappingExpr(GeneratorRequest $req, string $expr, ?string $validateExpr): string
+    {
+        $fallbackCase = SchemaToEnum::enumCaseName(self::FallbackValue);
+
+        return "(\\{$this->name()}::tryFrom({$expr}) ?? \\{$this->name()}::{$fallbackCase})";
+    }
+}