diff --git a/world/gmp/Makefile b/world/gmp/Makefile
index d1d8dee..b25067d 100644
--- a/world/gmp/Makefile
+++ b/world/gmp/Makefile
@@ -11,7 +11,7 @@ config_opts   += --enable-cxx
 config_opts   += --disable-static
 config_opts   += --docdir=$(install_prefix)/share/doc/gmp/$(gmp_version)
 
-install_cmd    ?= $(MAKE) -k $(makeflags) DESTDIR=$(DESTDIR) -C $(objdir) install || true
+install_cmd    = $(MAKE) -k $(makeflags) DESTDIR=$(DESTDIR) -C $(objdir) install || true
 
 post_install   = $(MAKE) DESTDIR=$(DESTDIR) -C $(objdir) html install-html
 
diff --git a/world/grub/Makefile b/world/grub/Makefile
index ba31c3f..7950546 100644
--- a/world/grub/Makefile
+++ b/world/grub/Makefile
@@ -8,6 +8,7 @@ config_opts += --sbindir=/sbin
 config_opts += --sysconfdir=/etc
 config_opts += --disable-efiemu
 config_opts += --disable-werror
+config_opts += --disable-device-mapper
 
 post_install = mv -v $(DESTDIR)/etc/bash_completion.d/grub $(DESTDIR)/usr/share/bash-completion/completions