diff --git a/package/heirloom-mailx/Config.in b/package/heirloom-mailx/Config.in
index 9a871d4..ca83dc3 100644
--- a/package/heirloom-mailx/Config.in
+++ b/package/heirloom-mailx/Config.in
@@ -1,5 +1,7 @@
 config BR2_PACKAGE_HEIRLOOM_MAILX
 	bool "heirloom-mailx"
+	# uses fork()
+	depends on BR2_USE_MMU
 	help
 	  Heirloom mailx (previously known as nail) is a mail user
 	  agent for Unix systems.