diff --git a/src/Headers.php b/src/Headers.php
index 23475bc..8cdb76f 100644
--- a/src/Headers.php
+++ b/src/Headers.php
@@ -278,10 +278,17 @@ class Headers implements Countable, Iterator
         }
 
         if ($fieldValue === null) {
-            $headers = $this->loadHeader($headerFieldNameOrLine);
-            $headers = is_array($headers) ? $headers : [$headers];
-            foreach ($headers as $header) {
-                $this->addHeader($header);
+            try {
+                $headers = $this->loadHeader($headerFieldNameOrLine);
+                $headers = is_array($headers) ? $headers : [$headers];
+                foreach ($headers as $header) {
+                    $this->addHeader($header);
+                }
+            } catch (\Laminas\Mail\Header\Exception\InvalidArgumentException $e) {
+                // Header line cannot be parsed, ignore it and add a warning
+                $parts = explode(':', $headerFieldNameOrLine, 2);
+                $msg = count($parts) !== 2 ? $e->getMessage() : sprintf('Invalid header "%s"', $parts[0]);
+                trigger_error($msg, E_USER_WARNING);
             }
         } elseif (is_array($fieldValue)) {
             foreach ($fieldValue as $i) {