diff --git a/procps/ps.c b/procps/ps.c
index 1f61753..4496faa 100644
--- a/procps/ps.c
+++ b/procps/ps.c
@@ -28,6 +28,9 @@
 #include <fcntl.h>
 #include <ctype.h>
 
+#if ! defined BB_FEATURE_USE_PROCFS
+#error Sorry, I depend on the /proc filesystem right now.
+#endif
 
 typedef struct proc_s {
     char