diff --git a/logback-classic-blackbox/src/test/java/ch/qos/logback/classic/blackbox/net/SMTPAppender_GreenTest.java b/logback-classic-blackbox/src/test/java/ch/qos/logback/classic/blackbox/net/SMTPAppender_GreenTest.java
index 741945c056..8cb0fd7e1b 100644
--- a/logback-classic-blackbox/src/test/java/ch/qos/logback/classic/blackbox/net/SMTPAppender_GreenTest.java
+++ b/logback-classic-blackbox/src/test/java/ch/qos/logback/classic/blackbox/net/SMTPAppender_GreenTest.java
@@ -168,8 +168,8 @@ void waitUntilEmailIsSent() throws InterruptedException {
         ExecutorService es = loggerContext.getExecutorService();
         es.shutdown();
         boolean terminated = es.awaitTermination(TIMEOUT, TimeUnit.MILLISECONDS);
+
         // this assertion may be needlessly strict, skipped on MacOS
-        System.getProperty("os.name");
         if(!terminated && !EnvUtil.isMacOs()) {
             fail("executor elapsed before accorded delay " + System.getProperty("os.name"));
         }
diff --git a/logback-core/src/main/java/ch/qos/logback/core/util/EnvUtil.java b/logback-core/src/main/java/ch/qos/logback/core/util/EnvUtil.java
index 9d833bff99..68a4091fa1 100644
--- a/logback-core/src/main/java/ch/qos/logback/core/util/EnvUtil.java
+++ b/logback-core/src/main/java/ch/qos/logback/core/util/EnvUtil.java
@@ -128,7 +128,7 @@ static public boolean isJaninoAvailable() {
 
     public static boolean isMacOs() {
         String os = System.getProperty("os.name");
-        return os.contains("mac");
+        return os.toLowerCase().contains("mac");
     }
 
     public static boolean isWindows() {