diff --git a/src/Headers.php b/src/Headers.php
index 8f406494..4aacd4b8 100644
--- a/src/Headers.php
+++ b/src/Headers.php
@@ -373,7 +373,7 @@ public function get($name)
         $key = $this->normalizeFieldName($name);
         $results = [];
 
-        foreach (array_keys($this->headersKeys, $key) as $index) {
+        foreach (array_keys($this->headersKeys, $key, true) as $index) {
             if ($this->headers[$index] instanceof Header\GenericHeader) {
                 $results[] = $this->lazyLoadHeader($index);
             } else {
@@ -403,7 +403,7 @@ public function get($name)
     public function has($name)
     {
         $name = $this->normalizeFieldName($name);
-        return in_array($name, $this->headersKeys);
+        return in_array($name, $this->headersKeys, true);
     }
 
     /**
diff --git a/test/HeadersTest.php b/test/HeadersTest.php
index 85ea0385..8a8f93aa 100644
--- a/test/HeadersTest.php
+++ b/test/HeadersTest.php
@@ -634,4 +634,16 @@ public function testCanInjectAlternateHeaderLocatorInstance(): void
         $headers->setHeaderLocator($locator);
         $this->assertSame($locator, $headers->getHeaderLocator());
     }
+
+    public function testStrictKeyComparisonInHas(): void
+    {
+        $headers = Mail\Headers::fromString("000: foo-bar");
+        $this->assertFalse($headers->has('0'));
+    }
+
+    public function testStrictKeyComparisonInGet(): void
+    {
+        $headers = Mail\Headers::fromString("000: foo-bar");
+        $this->assertFalse($headers->get('0'));
+    }
 }