diff --git a/src/Constrict/ConstrictResponse.php b/src/Constrict/ConstrictResponse.php
index c6e9a89..9d54960 100644
--- a/src/Constrict/ConstrictResponse.php
+++ b/src/Constrict/ConstrictResponse.php
@@ -97,7 +97,8 @@ class ConstrictResponse extends Message implements ResponseInterface
      */
     public function json(array $content, int $statusCode = 200): static
     {
-        $this->stream->write(json_encode($content, JSON_UNESCAPED_UNICODE));
+        $encoded = json_encode($content, JSON_UNESCAPED_UNICODE | JSON_INVALID_UTF8_SUBSTITUTE);
+        $this->stream->write($encoded === false ? '{"error":"json encode failed"}' : $encoded);
         return $this->withContentType(ContentType::JSON)->withStatus($statusCode);
     }
 
diff --git a/src/Format/ArrayFormat.php b/src/Format/ArrayFormat.php
index 701191b..3173877 100644
--- a/src/Format/ArrayFormat.php
+++ b/src/Format/ArrayFormat.php
@@ -25,7 +25,8 @@ class ArrayFormat implements IFormat
 	 */
 	public function call($result): ResponseInterface
 	{
-		return $this->response->withBody(new Stream(json_encode($result, JSON_UNESCAPED_UNICODE)));
+		$encoded = json_encode($result, JSON_UNESCAPED_UNICODE | JSON_INVALID_UTF8_SUBSTITUTE);
+		return $this->response->withBody(new Stream($encoded === false ? '[]' : $encoded));
 	}
 
 
diff --git a/src/Format/MixedFormat.php b/src/Format/MixedFormat.php
index 72e364b..a711f82 100644
--- a/src/Format/MixedFormat.php
+++ b/src/Format/MixedFormat.php
@@ -31,7 +31,8 @@ class MixedFormat implements IFormat
             return $this->response->withBody(new Stream('[object]'));
         }
         if (is_array($result)) {
-            return $this->response->withBody(new Stream(json_encode($result, JSON_UNESCAPED_UNICODE)));
+            $encoded = json_encode($result, JSON_UNESCAPED_UNICODE | JSON_INVALID_UTF8_SUBSTITUTE);
+            return $this->response->withBody(new Stream($encoded === false ? '[]' : $encoded));
         } else {
             return $this->response->withBody(new Stream((string)$result));
         }