diff --git a/src/copy_interpreter_to_host.c b/src/copy_interpreter_to_host.c
index d3afbea0e2ae06e24ed8fb6b78f4d43a313590a7..3771306308bf4d62fe97ad6aca972f7bce9d0564 100644
--- a/src/copy_interpreter_to_host.c
+++ b/src/copy_interpreter_to_host.c
@@ -65,7 +65,7 @@ struct interpretation_environment *build_interpretation_environment(
 	ie->bsp = bsp;
 	ie->csp = csp;
 	ie->hp = hp;
-	ie->hp_end = hp+heap_size;
+	ie->hp_end = hp+(heap_size>>1);
 	ie->caf_list[0] = 0;
 	ie->caf_list[1] = &ie->caf_list[1];
 	ie->options.in_first_semispace=1;