diff --git a/gc.c b/gc.c
index e5c7821f..3934a6c9 100644
--- a/gc.c
+++ b/gc.c
@@ -111,6 +111,9 @@ void sexp_conservative_mark (sexp ctx) {
           fprintf(stderr, "GC MISS: %p: %s\n", p, sexp_pointer_source(p));
           fflush(stderr);
         }
+#endif
+#if SEXP_USE_CONSERVATIVE_GC_PRESERVE_TAG
+        if (sexp_pointer_tag(p) == SEXP_USE_CONSERVATIVE_GC_PRESERVE_TAG)
 #endif
         sexp_mark(ctx, p);
       }
diff --git a/include/chibi/features.h b/include/chibi/features.h
index 02e42ddf..ad3d06eb 100644
--- a/include/chibi/features.h
+++ b/include/chibi/features.h
@@ -309,6 +309,10 @@
 #define SEXP_USE_CONSERVATIVE_GC SEXP_USE_DEBUG_GC > 1
 #endif
 
+#ifndef SEXP_USE_CONSERVATIVE_GC_PRESERVE_TAG
+#define SEXP_USE_CONSERVATIVE_GC_PRESERVE_TAG 0
+#endif
+
 #ifndef SEXP_USE_TRACK_ALLOC_SOURCE
 #define SEXP_USE_TRACK_ALLOC_SOURCE SEXP_USE_DEBUG_GC > 1
 #endif