diff --git a/api/FontFaceSet.json b/api/FontFaceSet.json
index 23fb615d7d1761..40cb4ca95895b0 100644
--- a/api/FontFaceSet.json
+++ b/api/FontFaceSet.json
@@ -443,7 +443,9 @@
             "opera": "mirror",
             "opera_android": "mirror",
             "safari": {
-              "version_added": "10"
+              "version_added": "10",
+              "partial_implementation": true,
+              "notes": "The `onloading` event handler is supported, but the event never fires. See [bug 304091](https://webkit.org/b/304091)."
             },
             "safari_ios": "mirror",
             "samsunginternet_android": "mirror",
@@ -479,7 +481,9 @@
             "opera": "mirror",
             "opera_android": "mirror",
             "safari": {
-              "version_added": "10"
+              "version_added": "10",
+              "partial_implementation": true,
+              "notes": "The `onloadingdone` event handler is supported, but the event never fires. See [bug 304091](https://webkit.org/b/304091)."
             },
             "safari_ios": "mirror",
             "samsunginternet_android": "mirror",
@@ -515,7 +519,9 @@
             "opera": "mirror",
             "opera_android": "mirror",
             "safari": {
-              "version_added": "10"
+              "version_added": "10",
+              "partial_implementation": true,
+              "notes": "The `onloadingerror` event handler is supported, but the event never fires. See [bug 304091](https://webkit.org/b/304091)."
             },
             "safari_ios": "mirror",
             "samsunginternet_android": "mirror",