ps/display.c:65:7: warning: implicit declaration of function ‘error_at_line’ [-Wimplicit-function-declaration]

--- ps/display.c
+++ ps/display.c
@@ -25,6 +25,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <error.h> /* error_at_line */
 
 #include <sys/sysmacros.h>
 #include <sys/types.h>