diff --git a/NEWS b/NEWS
index 63fa042a3..995fafb77 100644
--- a/NEWS
+++ b/NEWS
@@ -23,6 +23,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   "Too many levels of symbolic links" diagnostic.
   [bug introduced in coreutils-8.6]
 
+** Changes in behavior
+
+  nproc now diagnoses with an error, non option command line parameters.
+
 ** Improvements
 
   stat and tail work better with ZFS and VZFS.  stat -f --format=%T now
diff --git a/src/nproc.c b/src/nproc.c
index a93ee536b..98a1b9aca 100644
--- a/src/nproc.c
+++ b/src/nproc.c
@@ -24,6 +24,7 @@
 #include "system.h"
 #include "error.h"
 #include "nproc.h"
+#include "quote.h"
 #include "xstrtol.h"
 
 /* The official name of this program (e.g., no 'g' prefix).  */
@@ -113,6 +114,12 @@ main (int argc, char **argv)
         }
     }
 
+  if (argc != optind)
+    {
+      error (0, 0, _("extra operand %s"), quote (argv[optind]));
+      usage (EXIT_FAILURE);
+    }
+
   nproc = num_processors (mode);
 
   if (ignore < nproc)