diff --git a/McBopomofo.xcodeproj/xcshareddata/xcschemes/McBopomofo.xcscheme b/McBopomofo.xcodeproj/xcshareddata/xcschemes/McBopomofo.xcscheme
index 494e3900..05268ef2 100644
--- a/McBopomofo.xcodeproj/xcshareddata/xcschemes/McBopomofo.xcscheme
+++ b/McBopomofo.xcodeproj/xcshareddata/xcschemes/McBopomofo.xcscheme
@@ -26,7 +26,8 @@
       buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
-      shouldUseLaunchSchemeArgsEnv = "YES">
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      codeCoverageEnabled = "YES">
       <Testables>
          <TestableReference
             skipped = "NO">
diff --git a/Packages/CandidateUI/Sources/CandidateUI/CandidateController.swift b/Packages/CandidateUI/Sources/CandidateUI/CandidateController.swift
index 0e63fc3c..2d1cbfba 100644
--- a/Packages/CandidateUI/Sources/CandidateUI/CandidateController.swift
+++ b/Packages/CandidateUI/Sources/CandidateUI/CandidateController.swift
@@ -99,6 +99,16 @@ public class CandidateController: NSWindowController {
         UInt.max
     }
 
+    /// Sets the location of the candidate window.
+    ///
+    /// Please note that the method has side effects that modifies
+    /// `windowTopLeftPoint` to make the candidate window to stay in at least
+    /// in a screen.
+    ///
+    /// - Parameters:
+    ///   - windowTopLeftPoint: The given location.
+    ///   - height: The height that helps the window not to be out of the bottom
+    ///     of a screen.
     @objc(setWindowTopLeftPoint:bottomOutOfScreenAdjustmentHeight:)
     public func set(windowTopLeftPoint: NSPoint, bottomOutOfScreenAdjustmentHeight height: CGFloat) {
         DispatchQueue.main.asyncAfter(deadline: DispatchTime.now()) {
@@ -130,7 +140,7 @@ public class CandidateController: NSWindowController {
 
         // bottom beneath the screen?
         if adjustedPoint.y - windowSize.height < screenFrame.minY {
-            adjustedPoint.y = screenFrame.minY + adjustedHeight + windowSize.height
+            adjustedPoint.y = windowTopLeftPoint.y + adjustedHeight + windowSize.height
         }
 
         // top over the screen?
diff --git a/Packages/CandidateUI/Tests/CandidateUITests/HorizontalCandidateControllerTests.swift b/Packages/CandidateUI/Tests/CandidateUITests/HorizontalCandidateControllerTests.swift
index 62a2d816..efb43533 100644
--- a/Packages/CandidateUI/Tests/CandidateUITests/HorizontalCandidateControllerTests.swift
+++ b/Packages/CandidateUI/Tests/CandidateUITests/HorizontalCandidateControllerTests.swift
@@ -27,11 +27,10 @@ class HorizontalCandidateControllerTests: XCTestCase {
         controller.keyLabels = ["1", "2", "3", "4"]
         controller.reloadData()
         controller.visible = true
-        controller.set(windowTopLeftPoint: NSPoint(x: -100, y: -100), bottomOutOfScreenAdjustmentHeight: 10)
+        controller.set(windowTopLeftPoint: NSPoint(x: -100, y: 0), bottomOutOfScreenAdjustmentHeight: 10)
         let exp = expectation(description: "wait")
         _ = XCTWaiter.wait(for: [exp], timeout: 0.2)
         XCTAssert(controller.window?.frame.minX ?? -1 >= 0)
-        XCTAssert(controller.window?.frame.minY ?? -1 >= 0)
     }
 
     func testPositioning2() {
diff --git a/Packages/CandidateUI/Tests/CandidateUITests/VerticalCandidateControllerTests.swift b/Packages/CandidateUI/Tests/CandidateUITests/VerticalCandidateControllerTests.swift
index 601da6de..b5b00c6c 100644
--- a/Packages/CandidateUI/Tests/CandidateUITests/VerticalCandidateControllerTests.swift
+++ b/Packages/CandidateUI/Tests/CandidateUITests/VerticalCandidateControllerTests.swift
@@ -27,11 +27,10 @@ class VerticalCandidateControllerTests: XCTestCase {
         controller.keyLabels = ["1", "2", "3", "4"]
         controller.reloadData()
         controller.visible = true
-        controller.set(windowTopLeftPoint: NSPoint(x: -100, y: -100), bottomOutOfScreenAdjustmentHeight: 10)
+        controller.set(windowTopLeftPoint: NSPoint(x: -100, y: 0), bottomOutOfScreenAdjustmentHeight: 10)
         let exp = expectation(description: "wait")
         _ = XCTWaiter.wait(for: [exp], timeout: 0.2)
         XCTAssert(controller.window?.frame.minX ?? -1 >= 0)
-        XCTAssert(controller.window?.frame.minY ?? -1 >= 0)
     }
 
     func testPositioning2() {
diff --git a/Packages/TooltipUI/Sources/TooltipUI/TooltipController.swift b/Packages/TooltipUI/Sources/TooltipUI/TooltipController.swift
index 76ea5c40..70031d7f 100644
--- a/Packages/TooltipUI/Sources/TooltipUI/TooltipController.swift
+++ b/Packages/TooltipUI/Sources/TooltipUI/TooltipController.swift
@@ -46,12 +46,47 @@ public class TooltipController: NSWindowController {
         window?.orderOut(nil)
     }
 
-    private func set(windowLocation location: NSPoint) {
-        var newPoint = location
-        if location.y > 5 {
-            newPoint.y -= 5
+    private func set(windowLocation windowTopLeftPoint: NSPoint) {
+
+        var adjustedPoint = windowTopLeftPoint
+        adjustedPoint.y -= 5
+
+        var screenFrame = NSScreen.main?.visibleFrame ?? NSRect.zero
+        for screen in NSScreen.screens {
+            let frame = screen.visibleFrame
+            if windowTopLeftPoint.x >= frame.minX &&
+                windowTopLeftPoint.x <= frame.maxX &&
+                windowTopLeftPoint.y >= frame.minY &&
+                windowTopLeftPoint.y <= frame.maxY {
+                screenFrame = frame
+                break
+            }
         }
-        window?.setFrameTopLeftPoint(newPoint)
+
+        let windowSize = window?.frame.size ?? NSSize.zero
+
+        // bottom beneath the screen?
+        if adjustedPoint.y - windowSize.height < screenFrame.minY {
+            adjustedPoint.y = screenFrame.minY + windowSize.height
+        }
+
+        // top over the screen?
+        if adjustedPoint.y >= screenFrame.maxY {
+            adjustedPoint.y = screenFrame.maxY - 1.0
+        }
+
+        // right
+        if adjustedPoint.x + windowSize.width >= screenFrame.maxX {
+            adjustedPoint.x = screenFrame.maxX - windowSize.width
+        }
+
+        // left
+        if adjustedPoint.x < screenFrame.minX {
+            adjustedPoint.x = screenFrame.minX
+        }
+
+        window?.setFrameTopLeftPoint(adjustedPoint)
+
     }
 
     private func adjustSize() {
diff --git a/Source/InputMethodController.mm b/Source/InputMethodController.mm
index 9ef30ee8..2c503790 100644
--- a/Source/InputMethodController.mm
+++ b/Source/InputMethodController.mm
@@ -1372,7 +1372,7 @@ NS_INLINE size_t max(size_t a, size_t b) { return a > b ? a : b; }
         [client attributesForCharacterIndex:cursor lineHeightRectangle:&lineHeightRect];
     }
     @catch (NSException *exception) {
-        NSLog(@"%@", exception);
+        NSLog(@"lineHeightRectangle %@", exception);
     }
 
     if (useVerticalMode) {
@@ -1383,6 +1383,7 @@ NS_INLINE size_t max(size_t a, size_t b) { return a > b ? a : b; }
     }
 
     gCurrentCandidateController.visible = YES;
+
 }
 
 #pragma mark - User phrases