diff --git a/darwin/CMakeLists.txt b/darwin/CMakeLists.txt
index 253b621c..d03d0f0d 100644
--- a/darwin/CMakeLists.txt
+++ b/darwin/CMakeLists.txt
@@ -44,6 +44,7 @@ list(APPEND _LIBUI_SOURCES
 	darwin/stddialogs.m
 	darwin/tab.m
 	darwin/text.m
+	darwin/undocumented.m
 	darwin/util.m
 	darwin/window.m
 	darwin/winmoveresize.m
diff --git a/darwin/fontmatch.m b/darwin/fontmatch.m
index 6cec26b6..25476900 100644
--- a/darwin/fontmatch.m
+++ b/darwin/fontmatch.m
@@ -26,10 +26,6 @@
 // because the descriptors returned by Core Text's own font
 // matching won't have any.
 
-// TODO explicitly mark these as undocumented
-extern const CFStringRef kCTFontPreferredSubFamilyNameKey;
-extern const CFStringRef kCTFontPreferredFamilyNameKey;
-
 @implementation fontStyleData
 
 - (id)initWithFont:(CTFontRef)f
@@ -246,7 +242,7 @@ extern const CFStringRef kCTFontPreferredFamilyNameKey;
 FONTNAME(preferredSubFamilyName,
 	self->didPreferredSubFamilyName,
 	self->preferredSubFamilyName,
-	kCTFontPreferredSubFamilyNameKey)
+	UNDOC_kCTFontPreferredSubFamilyNameKey)
 FONTNAME(subFamilyName,
 	self->didSubFamilyName,
 	self->subFamilyName,
@@ -258,7 +254,7 @@ FONTNAME(fullName,
 FONTNAME(preferredFamilyName,
 	self->didPreferredFamilyName,
 	self->preferredFamilyName,
-	kCTFontPreferredFamilyNameKey)
+	UNDOC_kCTFontPreferredFamilyNameKey)
 FONTNAME(familyName,
 	self->didFamilyName,
 	self->familyName,
diff --git a/darwin/future.m b/darwin/future.m
index a6988f83..60936f40 100644
--- a/darwin/future.m
+++ b/darwin/future.m
@@ -4,8 +4,6 @@
 // functions and constants FROM THE FUTURE!
 // note: for constants, dlsym() returns the address of the constant itself, as if we had done &constantName
 
-// TODO add weight constants here?
-
 // added in OS X 10.10; we need 10.8
 CFStringRef *FUTURE_kCTFontOpenTypeFeatureTag = NULL;
 CFStringRef *FUTURE_kCTFontOpenTypeFeatureValue = NULL;
diff --git a/darwin/main.m b/darwin/main.m
index 60acecaf..d85000dd 100644
--- a/darwin/main.m
+++ b/darwin/main.m
@@ -120,6 +120,7 @@ const char *uiInit(uiInitOptions *o)
 
 		initAlloc();
 		loadFutures();
+		loadUndocumented();
 
 		// always do this so we always have an application menu
 		appDelegate().menuManager = [[menuManager new] autorelease];
diff --git a/darwin/uipriv_darwin.h b/darwin/uipriv_darwin.h
index 26366520..0303c32c 100644
--- a/darwin/uipriv_darwin.h
+++ b/darwin/uipriv_darwin.h
@@ -174,3 +174,8 @@ extern CFStringRef *FUTURE_kCTFontOpenTypeFeatureValue;
 extern void loadFutures(void);
 extern void FUTURE_NSLayoutConstraint_setIdentifier(NSLayoutConstraint *constraint, NSString *identifier);
 extern BOOL FUTURE_NSWindow_performWindowDragWithEvent(NSWindow *w, NSEvent *initialEvent);
+
+// undocumented.m
+extern CFStringRef UNDOC_kCTFontPreferredSubFamilyNameKey;
+extern CFStringRef UNDOC_kCTFontPreferredFamilyNameKey;
+extern void loadUndocumented(void);
diff --git a/darwin/undocumented.m b/darwin/undocumented.m
new file mode 100644
index 00000000..0e016dd6
--- /dev/null
+++ b/darwin/undocumented.m
@@ -0,0 +1,31 @@
+// 3 november 2017
+#import "uipriv_darwin.h"
+
+// functions and constants FROM THE DEPTHS BELOW!
+// note: for constants, dlsym() returns the address of the constant itself, as if we had done &constantName
+// we also provide default values just in case
+
+// these values come from 10.12.6
+CFStringRef UNDOC_kCTFontPreferredSubFamilyNameKey = CFSTR("CTFontPreferredSubFamilyName");
+CFStringRef UNDOC_kCTFontPreferredFamilyNameKey = CFSTR("CTFontPreferredFamilyName");
+
+// note that we treat any error as "the symbols aren't there" (and don't care if dlclose() failed)
+void loadUndocumented(void)
+{
+	void *handle;
+	CFStringRef *str;
+
+	// dlsym() walks the dependency chain, so opening the current process should be sufficient
+	handle = dlopen(NULL, RTLD_LAZY);
+	if (handle == NULL)
+		return;
+#define GET(var, fn) *((void **) (&var)) = dlsym(handle, #fn)
+	GET(str, kCTFontPreferredSubFamilyNameKey);
+NSLog(@"get %p", str);
+	if (str != NULL)
+		UNDOC_kCTFontPreferredSubFamilyNameKey = *str;
+	GET(str, kCTFontPreferredFamilyNameKey);
+	if (str != NULL)
+		UNDOC_kCTFontPreferredFamilyNameKey = *str;
+	dlclose(handle);
+}