diff --git a/modules/libpref/src/mac/MacPrefUtils.cpp b/modules/libpref/src/mac/MacPrefUtils.cpp
index fb196ae73af1..a2f4938abc57 100644
--- a/modules/libpref/src/mac/MacPrefUtils.cpp
+++ b/modules/libpref/src/mac/MacPrefUtils.cpp
@@ -29,6 +29,7 @@
 #include "plstr.h"
 #include "FullPath.h"
 #include "net.h"
+#include "xp_mem.h" // for XP_FREE
 
 // Returns a full pathname to the given file
 // Returned value is allocated with XP_ALLOC, and must be freed with XP_FREE