diff --git a/src/OpenTracing/Mock/MockSpanContext.php b/src/OpenTracing/Mock/MockSpanContext.php
index 6bc13b8..d094ea0 100644
--- a/src/OpenTracing/Mock/MockSpanContext.php
+++ b/src/OpenTracing/Mock/MockSpanContext.php
@@ -4,8 +4,8 @@
 
 namespace OpenTracing\Mock;
 
-use ArrayIterator;
 use OpenTracing\SpanContext;
+use ArrayIterator;
 
 final class MockSpanContext implements SpanContext
 {
@@ -88,7 +88,7 @@ public function getBaggageItem(string $key): ?string
     /**
      * {@inheritdoc}
      */
-    public function withBaggageItem(string $key, string $value): ?SpanContext
+    public function withBaggageItem(string $key, string $value): SpanContext
     {
         return new self($this->traceId, $this->spanId, $this->isSampled, array_merge($this->items, [$key => $value]));
     }
diff --git a/src/OpenTracing/NoopSpanContext.php b/src/OpenTracing/NoopSpanContext.php
index 8532bd2..b473412 100644
--- a/src/OpenTracing/NoopSpanContext.php
+++ b/src/OpenTracing/NoopSpanContext.php
@@ -27,7 +27,7 @@ public function getBaggageItem(string $key): ?string
     /**
      * {@inheritdoc}
      */
-    public function withBaggageItem(string $key, string $value): ?SpanContext
+    public function withBaggageItem(string $key, string $value): SpanContext
     {
         return new self();
     }
diff --git a/src/OpenTracing/SpanContext.php b/src/OpenTracing/SpanContext.php
index 75f1632..ca05ff9 100644
--- a/src/OpenTracing/SpanContext.php
+++ b/src/OpenTracing/SpanContext.php
@@ -33,5 +33,5 @@ public function getBaggageItem(string $key): ?string;
      * @param string $value
      * @return SpanContext
      */
-    public function withBaggageItem(string $key, string $value): ?SpanContext;
+    public function withBaggageItem(string $key, string $value): SpanContext;
 }