diff --git a/src/libcalamares/utils/Tests.cpp b/src/libcalamares/utils/Tests.cpp
index 0f7d6cd81..97edd0bc4 100644
--- a/src/libcalamares/utils/Tests.cpp
+++ b/src/libcalamares/utils/Tests.cpp
@@ -155,8 +155,10 @@ LibCalamaresTests::testUmask()
     QTemporaryFile ft;
     QVERIFY( ft.open() );
 
+    // m gets the previous value of the mask (depends on the environment the
+    // test is run in, might be 002, might be 077), ..
     mode_t m = CalamaresUtils::setUMask( 022 );
-    QCOMPARE( CalamaresUtils::setUMask( m ), m );
+    QCOMPARE( CalamaresUtils::setUMask( m ), 022 );  // But now most recently set was 022
 
     for ( mode_t i = 0; i <= 0777 /* octal! */; ++i )
     {
diff --git a/src/libcalamares/utils/UMask.h b/src/libcalamares/utils/UMask.h
index 58b1a56ad..752c8b066 100644
--- a/src/libcalamares/utils/UMask.h
+++ b/src/libcalamares/utils/UMask.h
@@ -25,7 +25,10 @@
 
 namespace CalamaresUtils
 {
-/// @brief Wrapper for umask(2)
+/** @brief Wrapper for umask(2)
+ *
+ * Like umask(2), sets the umask and returns the previous value of the mask.
+ */
 DLLEXPORT mode_t setUMask( mode_t u );
 
 /** @brief RAII for setting and re-setting umask.