diff --git a/clientscr/Mac_Saver_ModuleView.h b/clientscr/Mac_Saver_ModuleView.h
index 2cad85d0f1..af4c68bb78 100644
--- a/clientscr/Mac_Saver_ModuleView.h
+++ b/clientscr/Mac_Saver_ModuleView.h
@@ -43,6 +43,7 @@
 - (IBAction)closeSheetCancel:(id) sender;
 
 - (bool) setUpToUseCGWindowList;
+- (void) doPeriodicTasks;
 
 @end
 
diff --git a/clientscr/Mac_Saver_ModuleView.m b/clientscr/Mac_Saver_ModuleView.m
index 169e432c5b..20f08ab769 100644
--- a/clientscr/Mac_Saver_ModuleView.m
+++ b/clientscr/Mac_Saver_ModuleView.m
@@ -43,7 +43,7 @@
 // [7] In the Edit Scheme dialog Arguments tab, add "-debug" and "-window" to 
 //     "Arguments passed on launch"
 //
-// [8] In the Finder, open the directory "/Library/Screen Avers" and remove "BOINCSaver.saver"
+// [8] In the Finder, open the directory "/Library/Screen Savers" and remove "BOINCSaver.saver"
 //
 // [9] In Xcode's Project navigator, under "Products", control-click on "BOINCSaver.saver" and 
 //     select " Show in Finder"; make sure your are looking at the Development subdirectory.
@@ -157,6 +157,7 @@ static bool UseSharedOffscreenBuffer(void);
 static double lastGetSSMsgTime;
 static pthread_t mainThreadID;
 static int CGWindowListTries;
+static bool mojave;
 
 
 #define TEXTBOXMINWIDTH 400.0
@@ -198,6 +199,7 @@ void launchedGfxApp(char * appPath, pid_t thePID, int slot) {
 
 - (id)initWithFrame:(NSRect)frame isPreview:(BOOL)isPreview {
     self = [ super initWithFrame:frame isPreview:isPreview ];
+    mojave = (compareOSVersionTo(10, 14) >= 0);
     return self;
 }
 
@@ -213,6 +215,9 @@ void launchedGfxApp(char * appPath, pid_t thePID, int slot) {
     
     mainThreadID = pthread_self();
 
+    // Under OS 10.14 Mojave, [super drawRect:] is slow but not needed if we do this:
+    [[self window] setBackgroundColor:[NSColor blackColor]];
+
     initBOINCSaver();
 
     if (gBOINC_Logo == NULL) {
@@ -341,6 +346,18 @@ void launchedGfxApp(char * appPath, pid_t thePID, int slot) {
 - (void)stopAnimation {
     [ super stopAnimation ];
 
+    if ([ self isPreview ]) return;
+    NSRect windowFrame = [ [ self window ] frame ];
+    if ( (windowFrame.origin.x != 0) || (windowFrame.origin.y != 0) ) {
+        return;         // We draw only to main screen
+    }
+    if (imageView) {
+        useCGWindowList = false;
+        // removeFromSuperview must be called from main thread
+        [imageView removeFromSuperview];   // Releases imageView
+        imageView = nil;
+    }
+
     if ( ! [ self isPreview ] ) {
         closeBOINCSaver();
     }
@@ -360,15 +377,18 @@ void launchedGfxApp(char * appPath, pid_t thePID, int slot) {
 // multiple times (once for each display), so we need to guard 
 // against any problems that may cause.
 - (void)drawRect:(NSRect)rect {
-    [ super drawRect:rect ];
-
 //  optionally draw here
+    if (mojave) {
+        [self doPeriodicTasks];
+    } else {
+        [ super drawRect:rect ];
+    }
 }
 
 // If there are multiple displays, this may get called 
 // multiple times (once for each display), so we need to guard 
 // against any problems that may cause.
-- (void)animateOneFrame {
+- (void)doPeriodicTasks {
     int newFrequency = 0;
     int coveredFreq = 0;
     NSRect theFrame = [ self frame ];
@@ -472,8 +492,7 @@ void launchedGfxApp(char * appPath, pid_t thePID, int slot) {
         if (childApp) {
              if (![ childApp activateWithOptions:NSApplicationActivateIgnoringOtherApps ]) {
                 launchedGfxApp("", 0, -1);  // Graphics app is no longer running
-             }
-             if (useCGWindowList) {
+             } else if (useCGWindowList) {
                 // As a safety precaution, prevent terminating gfx app while copying its window
                 pthread_mutex_lock(&saver_mutex);
 
@@ -749,6 +768,22 @@ void launchedGfxApp(char * appPath, pid_t thePID, int slot) {
     }
 }
 
+
+- (void)animateOneFrame {
+    
+    NSRect windowFrame = [ [ self window ] frame ];
+    if ( (windowFrame.origin.x != 0) || (windowFrame.origin.y != 0) ) {
+        return;         // We draw only to main screen
+    }
+    //  Drawing in animateOneFrame doesn't seem to work under OS 10.14 Mojave
+    // but drawing in drawRect: seems slow under erarlier versions of OS X
+    if (mojave) {
+        [self display];
+    } else {
+        [self doPeriodicTasks];
+    }
+}
+
 - (BOOL)hasConfigureSheet {
     return YES;
 }