src/java.desktop/macosx/native/libawt_lwawt/awt/AWTWindow.m

@@ -317,10 +317,14 @@
 
     if (IS(self.styleBits, IS_POPUP)) {
         [self.nsWindow setCollectionBehavior:(1 << 8) /*NSWindowCollectionBehaviorFullScreenAuxiliary*/];
     }
 
+    if (IS(self.styleBits, SHEET)) {
+        [self.nsWindow setStyleMask: NSDocModalWindowMask];
+    }
+
     return self;
 }
 
 + (BOOL) isAWTWindow:(NSWindow *)window {
     return [window isKindOfClass: [AWTWindow_Panel class]] || [window isKindOfClass: [AWTWindow_Normal class]];