--- origsrc/procps-v4.0.4/src/ps/output.c
+++ src/procps-v4.0.4/src/ps/output.c
@@ -796,6 +796,8 @@ static int pr_wchan(char *restrict const
   size_t len;
 setREL1(WCHAN_NAME)
   w = rSv(WCHAN_NAME, str, pp);
+  if (!w)
+    w = "?";
   len = strlen(w);
   if(len>max_rightward) len=max_rightward;
   memcpy(outbuf, w, len);
