diff --git a/Source/WebKit/ChangeLog b/Source/WebKit/ChangeLog
index ff94b3c..d8f1cbe 100644
--- a/Source/WebKit/ChangeLog
+++ b/Source/WebKit/ChangeLog
@@ -1,3 +1,43 @@
+2019-07-15  Wenson Hsieh  <wenson_hsieh@apple.com>
+
+        [macOS 10.15] Cannot unbold selected text when the system font is used
+        https://bugs.webkit.org/show_bug.cgi?id=199788
+        <rdar://problem/52142570>
+
+        Reviewed by Tim Horton.
+
+        In macOS 10.15, +[NSFont fontWithName:size:] no longer recognizes system fonts (of name
+        ".SFNS-*") and returns nil instead. However, our existing implementation of
+        WebPageProxy::fontAtSelection works by grabbing the font name in the web process, and
+        sending it over to the UI process, where it is mapped to an NSFont. As a result, this always
+        results in a nil font in macOS 10.15, which causes us to never update NSFontManager's
+        selected font. In turn, this means that once selected text is bolded, it can't be unbolded
+        via NSFontManager, since NSFontManager thinks that the text is still not bold.
+
+        To fix this, we simply encode and send a platform FontInfo instead of sending the font name.
+        This allows the UI process to reconstruct NSFonts from font attribute dictionaries instead,
+        and update the font manager.
+
+        * UIProcess/Cocoa/WebViewImpl.mm:
+        (WebKit::WebViewImpl::updateFontManagerIfNeeded):
+        * UIProcess/WebPageProxy.h:
+        * UIProcess/WebPageProxy.messages.in:
+        * UIProcess/mac/WebPageProxyMac.mm:
+        (WebKit::WebPageProxy::fontAtSelection):
+
+        Refactor this to send a FontInfo (containing a font attribute dictionary) instead of a font
+        name.
+
+        (WebKit::WebPageProxy::fontAtSelectionCallback): Deleted.
+        * WebProcess/WebPage/WebPage.h:
+        * WebProcess/WebPage/WebPage.messages.in:
+
+        Change FontAtSelection to use sendWithAsyncReply instead of sending a callback ID. This also
+        allows us to remove FontAtSelectionCallback.
+
+        * WebProcess/WebPage/mac/WebPageMac.mm:
+        (WebKit::WebPage::fontAtSelection):
+
 2019-07-15  Jiewen Tan  <jiewen_tan@apple.com>
 
         [iOS] SOAuthorizationSession should tell AppSSO whether the UIClient is capable of showing the extension UI
diff --git a/Source/WebKit/UIProcess/Cocoa/WebViewImpl.mm b/Source/WebKit/UIProcess/Cocoa/WebViewImpl.mm
index bfd4334..8410992 100644
--- a/Source/WebKit/UIProcess/Cocoa/WebViewImpl.mm
+++ b/Source/WebKit/UIProcess/Cocoa/WebViewImpl.mm
@@ -34,6 +34,7 @@
 #import "AppKitSPI.h"
 #import "AttributedString.h"
 #import "ColorSpaceData.h"
+#import "FontInfo.h"
 #import "FullscreenClient.h"
 #import "GenericCallback.h"
 #import "InsertTextOptions.h"
@@ -2809,9 +2810,20 @@
     if (!fontPanelIsVisible && !m_page->editorState().isContentRichlyEditable)
         return;
 
-    m_page->fontAtSelection([](const String& fontName, double fontSize, bool selectionHasMultipleFonts, WebKit::CallbackBase::Error error) {
-        if (NSFont *font = [NSFont fontWithName:fontName size:fontSize])
-            [NSFontManager.sharedFontManager setSelectedFont:font isMultiple:selectionHasMultipleFonts];
+    m_page->fontAtSelection([](const FontInfo& fontInfo, double fontSize, bool selectionHasMultipleFonts) {
+        NSDictionary *attributeDictionary = (__bridge NSDictionary *)fontInfo.fontAttributeDictionary.get();
+        if (!attributeDictionary)
+            return;
+
+        NSFontDescriptor *descriptor = [NSFontDescriptor fontDescriptorWithFontAttributes:attributeDictionary];
+        if (!descriptor)
+            return;
+
+        NSFont *font = [NSFont fontWithDescriptor:descriptor size:fontSize];
+        if (!font)
+            return;
+
+        [NSFontManager.sharedFontManager setSelectedFont:font isMultiple:selectionHasMultipleFonts];
     });
 }
 
diff --git a/Source/WebKit/UIProcess/WebPageProxy.h b/Source/WebKit/UIProcess/WebPageProxy.h
index 7a59e4e..c9ba8c3 100644
--- a/Source/WebKit/UIProcess/WebPageProxy.h
+++ b/Source/WebKit/UIProcess/WebPageProxy.h
@@ -282,6 +282,7 @@
 struct DocumentEditingContextRequest;
 struct EditingRange;
 struct EditorState;
+struct FontInfo;
 struct FrameInfoData;
 struct InsertTextOptions;
 struct InteractionInformationRequest;
@@ -337,7 +338,6 @@
 
 #if PLATFORM(MAC)
 typedef GenericCallback<const AttributedString&, const EditingRange&> AttributedStringForCharacterRangeCallback;
-typedef GenericCallback<const String&, double, bool> FontAtSelectionCallback;
 #endif
 
 #if PLATFORM(IOS_FAMILY)
@@ -788,7 +788,7 @@
 #if PLATFORM(MAC)
     void insertDictatedTextAsync(const String& text, const EditingRange& replacementRange, const Vector<WebCore::TextAlternativeWithRange>& dictationAlternatives, bool registerUndoGroup);
     void attributedSubstringForCharacterRangeAsync(const EditingRange&, WTF::Function<void (const AttributedString&, const EditingRange&, CallbackBase::Error)>&&);
-    void fontAtSelection(WTF::Function<void (const String&, double, bool, CallbackBase::Error)>&&);
+    void fontAtSelection(Function<void(const FontInfo&, double, bool)>&&);
 
     void startWindowDrag();
     NSWindow *platformWindow();
@@ -1869,7 +1869,6 @@
     void rectForCharacterRangeCallback(const WebCore::IntRect&, const EditingRange&, CallbackID);
 #if PLATFORM(MAC)
     void attributedStringForCharacterRangeCallback(const AttributedString&, const EditingRange&, CallbackID);
-    void fontAtSelectionCallback(const String&, double, bool, CallbackID);
 #endif
 #if PLATFORM(IOS_FAMILY)
     void gestureCallback(const WebCore::IntPoint&, uint32_t gestureType, uint32_t gestureState, uint32_t flags, CallbackID);
diff --git a/Source/WebKit/UIProcess/WebPageProxy.messages.in b/Source/WebKit/UIProcess/WebPageProxy.messages.in
index 4163793..ff053df5 100644
--- a/Source/WebKit/UIProcess/WebPageProxy.messages.in
+++ b/Source/WebKit/UIProcess/WebPageProxy.messages.in
@@ -180,7 +180,6 @@
 #endif
 #if PLATFORM(MAC)
     AttributedStringForCharacterRangeCallback(struct WebKit::AttributedString string, struct WebKit::EditingRange actualRange, WebKit::CallbackID callbackID)
-    FontAtSelectionCallback(String fontName, double fontSize, bool selectioHasMultipleFonts, WebKit::CallbackID callbackID)
 #endif
     FontAttributesCallback(struct WebCore::FontAttributes attributes, WebKit::CallbackID callbackID)
 #if PLATFORM(IOS_FAMILY)
diff --git a/Source/WebKit/UIProcess/mac/WebPageProxyMac.mm b/Source/WebKit/UIProcess/mac/WebPageProxyMac.mm
index 87c68b3..311ec34 100644
--- a/Source/WebKit/UIProcess/mac/WebPageProxyMac.mm
+++ b/Source/WebKit/UIProcess/mac/WebPageProxyMac.mm
@@ -33,6 +33,7 @@
 #import "ColorSpaceData.h"
 #import "DataReference.h"
 #import "EditorState.h"
+#import "FontInfo.h"
 #import "InsertTextOptions.h"
 #import "MenuUtilities.h"
 #import "NativeWebKeyboardEvent.h"
@@ -240,28 +241,13 @@
     callback->performCallbackWithReturnValue(string, actualRange);
 }
 
-void WebPageProxy::fontAtSelection(WTF::Function<void (const String&, double, bool, CallbackBase::Error)>&& callbackFunction)
+void WebPageProxy::fontAtSelection(Function<void(const FontInfo&, double, bool)>&& callback)
 {
     if (!hasRunningProcess()) {
-        callbackFunction(String(), 0, false, CallbackBase::Error::Unknown);
+        callback({ }, 0, false);
         return;
     }
-    
-    auto callbackID = m_callbacks.put(WTFMove(callbackFunction), m_process->throttler().backgroundActivityToken());
-    
-    process().send(Messages::WebPage::FontAtSelection(callbackID), m_pageID);
-}
-
-void WebPageProxy::fontAtSelectionCallback(const String& fontName, double fontSize, bool selectionHasMultipleFonts, CallbackID callbackID)
-{
-    auto callback = m_callbacks.take<FontAtSelectionCallback>(callbackID);
-    if (!callback) {
-        // FIXME: Log error or assert.
-        // this can validly happen if a load invalidated the callback, though
-        return;
-    }
-    
-    callback->performCallbackWithReturnValue(fontName, fontSize, selectionHasMultipleFonts);
+    m_process->connection()->sendWithAsyncReply(Messages::WebPage::FontAtSelection(), WTFMove(callback), m_pageID);
 }
 
 String WebPageProxy::stringSelectionForPasteboard()
diff --git a/Source/WebKit/WebProcess/WebPage/WebPage.h b/Source/WebKit/WebProcess/WebPage/WebPage.h
index 97483e0..3ee3a89 100644
--- a/Source/WebKit/WebProcess/WebPage/WebPage.h
+++ b/Source/WebKit/WebProcess/WebPage/WebPage.h
@@ -258,6 +258,7 @@
 struct BackForwardListItemState;
 struct DataDetectionResult;
 struct EditorState;
+struct FontInfo;
 struct InsertTextOptions;
 struct InteractionInformationAtPosition;
 struct InteractionInformationRequest;
@@ -810,7 +811,7 @@
 #if PLATFORM(MAC)
     void insertDictatedTextAsync(const String& text, const EditingRange& replacementRange, const Vector<WebCore::DictationAlternative>& dictationAlternativeLocations, bool registerUndoGroup = false);
     void attributedSubstringForCharacterRangeAsync(const EditingRange&, CallbackID);
-    void fontAtSelection(CallbackID);
+    void fontAtSelection(CompletionHandler<void(const FontInfo&, double, bool)>&&);
 #endif
 
 #if PLATFORM(COCOA) && ENABLE(SERVICE_CONTROLS)
diff --git a/Source/WebKit/WebProcess/WebPage/WebPage.messages.in b/Source/WebKit/WebProcess/WebPage/WebPage.messages.in
index f31ee1d..06cff4e 100644
--- a/Source/WebKit/WebProcess/WebPage/WebPage.messages.in
+++ b/Source/WebKit/WebProcess/WebPage/WebPage.messages.in
@@ -445,7 +445,7 @@
 #if PLATFORM(MAC)
     InsertDictatedTextAsync(String text, struct WebKit::EditingRange replacementRange, Vector<WebCore::DictationAlternative> dictationAlternatives, bool registerUndoGroup)
     AttributedSubstringForCharacterRangeAsync(struct WebKit::EditingRange range, WebKit::CallbackID callbackID);
-    FontAtSelection(WebKit::CallbackID callbackID);
+    FontAtSelection() -> (struct WebKit::FontInfo info, double fontSize, bool hasMultipleFonts) Async
 #endif
 
     SetAlwaysShowsHorizontalScroller(bool alwaysShowsHorizontalScroller)
diff --git a/Source/WebKit/WebProcess/WebPage/mac/WebPageMac.mm b/Source/WebKit/WebProcess/WebPage/mac/WebPageMac.mm
index 6be0582..a0a9b3d 100644
--- a/Source/WebKit/WebProcess/WebPage/mac/WebPageMac.mm
+++ b/Source/WebKit/WebProcess/WebPage/mac/WebPageMac.mm
@@ -33,6 +33,7 @@
 #import "DataReference.h"
 #import "EditingRange.h"
 #import "EditorState.h"
+#import "FontInfo.h"
 #import "InjectedBundleHitTestResult.h"
 #import "PDFKitImports.h"
 #import "PDFPlugin.h"
@@ -376,22 +377,35 @@
     send(Messages::WebPageProxy::AttributedStringForCharacterRangeCallback(attributedString, rangeToSend, callbackID));
 }
 
-void WebPage::fontAtSelection(CallbackID callbackID)
+void WebPage::fontAtSelection(CompletionHandler<void(const FontInfo&, double, bool)>&& reply)
 {
-    String fontName;
-    double fontSize = 0;
     bool selectionHasMultipleFonts = false;
-    Frame& frame = m_page->focusController().focusedOrMainFrame();
-    
-    if (!frame.selection().selection().isNone()) {
-        if (auto* font = frame.editor().fontForSelection(selectionHasMultipleFonts)) {
-            if (auto ctFont = font->getCTFont()) {
-                fontName = adoptCF(CTFontCopyPostScriptName(ctFont)).get();
-                fontSize = CTFontGetSize(ctFont);
-            }
-        }
+    auto& frame = m_page->focusController().focusedOrMainFrame();
+
+    if (frame.selection().selection().isNone()) {
+        reply({ }, 0, false);
+        return;
     }
-    send(Messages::WebPageProxy::FontAtSelectionCallback(fontName, fontSize, selectionHasMultipleFonts, callbackID));
+
+    auto* font = frame.editor().fontForSelection(selectionHasMultipleFonts);
+    if (!font) {
+        reply({ }, 0, false);
+        return;
+    }
+
+    auto ctFont = font->getCTFont();
+    if (!ctFont) {
+        reply({ }, 0, false);
+        return;
+    }
+
+    auto fontDescriptor = adoptCF(CTFontCopyFontDescriptor(ctFont));
+    if (!fontDescriptor) {
+        reply({ }, 0, false);
+        return;
+    }
+
+    reply({ adoptCF(CTFontDescriptorCopyAttributes(fontDescriptor.get())) }, CTFontGetSize(ctFont), selectionHasMultipleFonts);
 }
     
 
diff --git a/Tools/ChangeLog b/Tools/ChangeLog
index 9b19636..a045022 100644
--- a/Tools/ChangeLog
+++ b/Tools/ChangeLog
@@ -1,3 +1,17 @@
+2019-07-15  Wenson Hsieh  <wenson_hsieh@apple.com>
+
+        [macOS 10.15] Cannot unbold selected text when the system font is used
+        https://bugs.webkit.org/show_bug.cgi?id=199788
+        <rdar://problem/52142570>
+
+        Reviewed by Tim Horton.
+
+        Add a new API test to verify that bolding and unbolding updates the
+        shared font manager's selected font.
+
+        * TestWebKitAPI/Tests/mac/FontManagerTests.mm:
+        (TestWebKitAPI::TEST):
+
 2019-07-15  Jiewen Tan  <jiewen_tan@apple.com>
 
         [iOS] SOAuthorizationSession should tell AppSSO whether the UIClient is capable of showing the extension UI
diff --git a/Tools/TestWebKitAPI/Tests/mac/FontManagerTests.mm b/Tools/TestWebKitAPI/Tests/mac/FontManagerTests.mm
index 723d3c0..447f28e 100644
--- a/Tools/TestWebKitAPI/Tests/mac/FontManagerTests.mm
+++ b/Tools/TestWebKitAPI/Tests/mac/FontManagerTests.mm
@@ -506,6 +506,37 @@
     EXPECT_NULL(attributes[NSBackgroundColorAttributeName]);
 }
 
+TEST(FontManagerTests, SetSelectedSystemFontAfterTogglingBold)
+{
+    NSFontManager *fontManager = NSFontManager.sharedFontManager;
+
+    auto webView = webViewForFontManagerTesting(NSFontManager.sharedFontManager, @"<body style='font-family: system-ui;' contenteditable>Foo</body>");
+    [webView selectWord:nil];
+    [webView waitForNextPresentationUpdate];
+    [webView waitForNextPresentationUpdate];
+    auto initialSelectedFont = retainPtr([fontManager selectedFont]);
+
+    [webView _synchronouslyExecuteEditCommand:@"ToggleBold" argument:nil];
+    [webView waitForNextPresentationUpdate];
+    auto selectedFontAfterBolding = retainPtr([fontManager selectedFont]);
+
+    [webView _synchronouslyExecuteEditCommand:@"ToggleBold" argument:nil];
+    [webView waitForNextPresentationUpdate];
+    auto selectedFontAfterUnbolding = retainPtr([fontManager selectedFont]);
+
+    [webView _synchronouslyExecuteEditCommand:@"ToggleBold" argument:nil];
+    [webView waitForNextPresentationUpdate];
+    auto selectedFontAfterBoldingAgain = retainPtr([fontManager selectedFont]);
+
+    EXPECT_WK_STREQ([initialSelectedFont fontName], [selectedFontAfterUnbolding fontName]);
+    EXPECT_WK_STREQ([selectedFontAfterBolding fontName], [selectedFontAfterBoldingAgain fontName]);
+    EXPECT_FALSE([[initialSelectedFont fontName] isEqual:[selectedFontAfterBolding fontName]]);
+    EXPECT_EQ([initialSelectedFont pointSize], 16.);
+    EXPECT_EQ([selectedFontAfterBolding pointSize], 16.);
+    EXPECT_EQ([selectedFontAfterUnbolding pointSize], 16.);
+    EXPECT_EQ([selectedFontAfterBoldingAgain pointSize], 16.);
+}
+
 } // namespace TestWebKitAPI
 
 #endif // PLATFORM(MAC)