diff --git a/ChangeLog b/ChangeLog
index ec712a9..91a272a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,10 @@
 
 = Revision history for ruby-filemagic
 
+== Unreleased []
+
+* Remove Warning 'warning: undefining the allocator of T_DATA class FileMagic'
+
 == 0.7.3 [2022-01-07]
 
 * Dockerfile to build native extension (pull request #26 by Pavel Lobashov).
diff --git a/ext/filemagic/filemagic.c b/ext/filemagic/filemagic.c
index f63b8c2..aaa0013 100644
--- a/ext/filemagic/filemagic.c
+++ b/ext/filemagic/filemagic.c
@@ -210,6 +210,7 @@ void
 Init_ruby_filemagic() {
   char version[8] = "0";
   cFileMagic = rb_define_class("FileMagic", rb_cObject);
+  rb_undef_alloc_func(cFileMagic);
 
 #if defined(FILE_VERSION_MAJOR)
   RB_MAGIC_SET_VERSION(FILE_VERSION_MAJOR, patchlevel)