diff --git a/src/Imitation/java/lang/Math.php b/src/Imitation/java/lang/Math.php
index c0df91dd..575cb28e 100644
--- a/src/Imitation/java/lang/Math.php
+++ b/src/Imitation/java/lang/Math.php
@@ -16,4 +16,16 @@ public static function abs($number)
     {
         return abs($number);
     }
+
+    /**
+     * This decrease 1 from parameters
+     *
+     * @see https://docs.oracle.com/javase/jp/8/docs/api/java/lang/Math.html#decrementExact-int-
+     * @param int $a
+     * @return int
+     */
+    public static function decrementExact($a)
+    {
+        return $a - 1;
+    }
 }
diff --git a/tests/ImitateJavaLangMathTest.php b/tests/ImitateJavaLangMathTest.php
new file mode 100644
index 00000000..c7c8b9ea
--- /dev/null
+++ b/tests/ImitateJavaLangMathTest.php
@@ -0,0 +1,27 @@
+<?php
+namespace PHPJava\Tests;
+
+use PHPJava\Core\JavaArchive;
+use PHPUnit\Framework\TestCase;
+
+class ImitateJavaLangMathTest extends Base
+{
+    protected $fixtures = [
+        'ImitateJavaLangMathTest',
+    ];
+
+    public function testDecrementExact()
+    {
+        ob_start();
+        $this->initiatedJavaClasses['ImitateJavaLangMathTest']
+            ->getInvoker()
+            ->getStatic()
+            ->getMethods()
+            ->call(
+                'decrementExact',
+                1234
+            );
+        $value = (int) ob_get_clean();
+        $this->assertEquals(1233, $value);
+    }
+}
diff --git a/tests/fixtures/java/ImitateJavaLangMathTest.java b/tests/fixtures/java/ImitateJavaLangMathTest.java
new file mode 100644
index 00000000..ea6e220d
--- /dev/null
+++ b/tests/fixtures/java/ImitateJavaLangMathTest.java
@@ -0,0 +1,7 @@
+class ImitateJavaLangMathTest
+{
+    public static void decrementExact(int a)
+    {
+        System.out.println(Math.decrementExact(a));
+    }
+}