--- old/src/java.desktop/macosx/native/libawt_lwawt/awt/AWTWindow.m	2018-10-10 15:21:14.000000000 +0530
+++ new/src/java.desktop/macosx/native/libawt_lwawt/awt/AWTWindow.m	2018-10-10 15:21:14.000000000 +0530
@@ -319,6 +319,10 @@
         [self.nsWindow setCollectionBehavior:(1 << 8) /*NSWindowCollectionBehaviorFullScreenAuxiliary*/];
     }
 
+    if (IS(self.styleBits, SHEET)) {
+        [self.nsWindow setStyleMask: NSDocModalWindowMask];
+    }
+
     return self;
 }