diff --git a/src/hb-coretext.cc b/src/hb-coretext.cc
index 6c0525b..c18e33f 100644
--- a/src/hb-coretext.cc
+++ b/src/hb-coretext.cc
@@ -34,6 +34,10 @@
 
 #include "hb-coretext.hh"
 
+// conda-forge: it appears that this function was added in 10.13 (the SDK version we use
+// as of 2025-03) but not added to the headers until 10.15. It's used below and has a simple
+// prototype, so we just manually declare it:
+extern "C" CFArrayRef CTFontManagerCreateFontDescriptorsFromData(CFDataRef data);
 
 /**
  * SECTION:hb-coretext