diff --git a/coregrind/m_syswrap/syswrap-amd64-linux.c b/coregrind/m_syswrap/syswrap-amd64-linux.c
index 0f2ad8c51..407af7f76 100644
--- a/coregrind/m_syswrap/syswrap-amd64-linux.c
+++ b/coregrind/m_syswrap/syswrap-amd64-linux.c
@@ -249,6 +249,7 @@ PRE(sys_rt_sigreturn)
 PRE(sys_arch_prctl)
 {
    ThreadState* tst;
+   Bool known_option = True;
    PRINT( "arch_prctl ( %ld, %lx )", SARG1, ARG2 );
 
    vg_assert(VG_(is_valid_tid)(tid));
@@ -283,13 +284,16 @@ PRE(sys_arch_prctl)
       POST_MEM_WRITE(ARG2, sizeof(unsigned long));
    }
    else {
-      VG_(core_panic)("Unsupported arch_prctl option");
+      known_option = False;
    }
 
    /* Note; the Status writeback to guest state that happens after
       this wrapper returns does not change guest_FS_CONST or guest_GS_CONST;
       hence that direct assignment to the guest state is safe here. */
-   SET_STATUS_Success( 0 );
+   if (known_option)
+      SET_STATUS_Success( 0 );
+   else
+      SET_STATUS_Failure( VKI_EINVAL );
 }
 
 // Parts of this are amd64-specific, but the *PEEK* cases are generic.