diff --git a/src/HL7/Segments/MSH.php b/src/HL7/Segments/MSH.php
index b196096..d051b8e 100644
--- a/src/HL7/Segments/MSH.php
+++ b/src/HL7/Segments/MSH.php
@@ -128,26 +128,23 @@ public function setSecurity($value, int $position = 8)
      *
      * Sets message type to MSH segment.
      *
-     * If trigger event is already set, then it is preserved
+     * Note: If trigger event is already set, then it is preserved
      *
-     * Example:
-     *
-     * If field value is ORU^R01 and you call
-     *
-     * ```
-     * $msh->setMessageType('ORM');
-     * ```
+     * Example: If field value is ORU^R01 and you call $msh->setMessageType('ORM'), then the new field value will be
+     * ORM^R01. If it was empty then the new value will be just ORM.
      *
-     * Then the new field value will be ORM^R01.
-     * If it was empty then the new value will be just ORM.
-     *
-     * @param string $value
+     * Ref: https://hl7-definition.caristix.com/v2/HL7v2.5/Fields/MSH.9
+     * @param string|array<int, string> $value
      */
     public function setMessageType($value, int $position = 9): bool
     {
         $typeField = $this->getField($position);
-        if (is_array($typeField) && !empty($typeField[1])) {
-            $value = [$value, $typeField[1]];
+        if (is_array($typeField)) {
+            if (!empty($typeField[2])) {
+                $value = [$value, $typeField[1], $typeField[2]];
+            } elseif (!empty($typeField[1])) {
+                $value = [$value, $typeField[1]];
+            }
         }
         return $this->setField($position, $value);
     }
diff --git a/tests/Segments/MSHTest.php b/tests/Segments/MSHTest.php
index 930a9cd..8a23949 100644
--- a/tests/Segments/MSHTest.php
+++ b/tests/Segments/MSHTest.php
@@ -79,4 +79,38 @@ public function index_2_in_MSH_accepts_only_4_character_strings(): void
         $msh->setField(2, 'yyyyy');
         self::assertSame('xxxx', $msh->getField(2), 'Special fields not changed');
     }
+
+    /** @test */
+    public function messageType_can_be_set_in_message(): void
+    {
+        $msh = new MSH();
+        $msh->setMessageType('ORM');
+        self::assertSame('ORM', $msh->getField(9));
+        $msh->setMessageType('ORM^O01');
+        self::assertSame('ORM^O01', $msh->getField(9));
+
+        $msh = new MSH();
+        $msh->setMessageType(['ORU', 'R01']); // For v2.3
+        self::assertSame(['ORU', 'R01'], $msh->getField(9));
+
+        $msh = new MSH();
+        $msh->setMessageType(['ORU', 'R01', 'ORU_R01']); // For 2.5
+        self::assertSame(['ORU', 'R01', 'ORU_R01'], $msh->getField(9));
+    }
+
+    /** @test */
+    public function messageType_can_be_changed_in_message(): void
+    {
+        // For v2.3...
+        $msh = new MSH();
+        $msh->setMessageType(['ORU', 'R01']);
+        $msh->setMessageType('ORM');
+        self::assertSame(['ORM', 'R01'], $msh->getField(9));
+
+        // For v2.5...
+        $msh = new MSH();
+        $msh->setMessageType(['ORU', 'R01', 'ORU_R01']);
+        $msh->setMessageType('ORM');
+        self::assertSame(['ORM', 'R01', 'ORU_R01'], $msh->getField(9));
+    }
 }