diff -ur lablgtk-2.18.8.old/src/wrappers.h lablgtk-2.18.8.fix/src/wrappers.h
--- lablgtk-2.18.8.old/src/wrappers.h	2019-04-25 08:50:43.000000000 +0100
+++ lablgtk-2.18.8.fix/src/wrappers.h	2020-01-19 12:30:04.618485205 +0000
@@ -33,7 +33,7 @@
 #include <caml/mlvalues.h>
 #include <caml/fail.h>
 #include <caml/custom.h>
-CAMLextern char *young_start, *young_end; /* from minor_gc.h */
+//CAMLextern char *young_start, *young_end; /* from minor_gc.h */
 
 CAMLexport value copy_memblock_indirected (void *src, asize_t size);
 value alloc_memblock_indirected (asize_t size);