diff --git a/libc/bionic/sysconf.cpp b/libc/bionic/sysconf.cpp
index 7be0ab7..4a23fec 100644
--- a/libc/bionic/sysconf.cpp
+++ b/libc/bionic/sysconf.cpp
@@ -29,10 +29,10 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
-#include <linux/uio.h>  // For UIO_MAXIOV.
 #include <pthread.h>
 #include <stdio.h>  // For FOPEN_MAX.
 #include <sys/auxv.h>
+#include <sys/param.h>
 #include <sys/resource.h>
 #include <sys/sysinfo.h>
 #include <time.h>
@@ -48,18 +48,39 @@
 
 long sysconf(int name) {
   switch (name) {
-    case _SC_ARG_MAX:           return ARG_MAX;
+    //
+    // Things we actually have to calculate...
+    //
+    case _SC_ARG_MAX:
+      // Not a constant since Linux 2.6.23; see fs/exec.c for details.
+      // At least 32 pages, otherwise a quarter of the stack limit.
+      return MAX(__sysconf_rlimit(RLIMIT_STACK) / 4, _KERNEL_ARG_MAX);
+
+    case _SC_AVPHYS_PAGES:      return get_avphys_pages();
+    case _SC_CHILD_MAX:         return __sysconf_rlimit(RLIMIT_NPROC);
+    case _SC_CLK_TCK:           return static_cast<long>(getauxval(AT_CLKTCK));
+    case _SC_NPROCESSORS_CONF:  return get_nprocs_conf();
+    case _SC_NPROCESSORS_ONLN:  return get_nprocs();
+    case _SC_OPEN_MAX:          return __sysconf_rlimit(RLIMIT_NOFILE);
+
+    case _SC_PAGESIZE:
+    case _SC_PAGE_SIZE:
+      // _SC_PAGESIZE and _SC_PAGE_SIZE are distinct, but return the same value.
+      return static_cast<long>(getauxval(AT_PAGESZ));
+
+    case _SC_PHYS_PAGES:        return get_phys_pages();
+
+    //
+    // Constants...
+    //
     case _SC_BC_BASE_MAX:       return _POSIX2_BC_BASE_MAX;   // Minimum requirement.
     case _SC_BC_DIM_MAX:        return _POSIX2_BC_DIM_MAX;    // Minimum requirement.
     case _SC_BC_SCALE_MAX:      return _POSIX2_BC_SCALE_MAX;  // Minimum requirement.
     case _SC_BC_STRING_MAX:     return _POSIX2_BC_STRING_MAX; // Minimum requirement.
-    case _SC_CHILD_MAX:         return __sysconf_rlimit(RLIMIT_NPROC);
-    case _SC_CLK_TCK:           return static_cast<long>(getauxval(AT_CLKTCK));
     case _SC_COLL_WEIGHTS_MAX:  return _POSIX2_COLL_WEIGHTS_MAX;  // Minimum requirement.
     case _SC_EXPR_NEST_MAX:     return _POSIX2_EXPR_NEST_MAX;     // Minimum requirement.
     case _SC_LINE_MAX:          return _POSIX2_LINE_MAX;          // Minimum requirement.
     case _SC_NGROUPS_MAX:       return NGROUPS_MAX;
-    case _SC_OPEN_MAX:          return __sysconf_rlimit(RLIMIT_NOFILE);
     case _SC_PASS_MAX:          return PASS_MAX;
     case _SC_2_C_BIND:          return _POSIX2_C_BIND;
     case _SC_2_C_DEV:           return _POSIX2_C_DEV;
@@ -84,12 +105,7 @@
     case _SC_XOPEN_REALTIME_THREADS: return _XOPEN_REALTIME_THREADS;
     case _SC_XOPEN_LEGACY:      return _XOPEN_LEGACY;
     case _SC_ATEXIT_MAX:        return LONG_MAX;    // Unlimited.
-    case _SC_IOV_MAX:           return UIO_MAXIOV;
-
-    // _SC_PAGESIZE and _SC_PAGE_SIZE are distinct, but return the same value.
-    case _SC_PAGESIZE:
-    case _SC_PAGE_SIZE:
-      return static_cast<long>(getauxval(AT_PAGESZ));
+    case _SC_IOV_MAX:           return IOV_MAX;
 
     case _SC_XOPEN_UNIX:        return _XOPEN_UNIX;
     case _SC_AIO_LISTIO_MAX:    return _POSIX_AIO_LISTIO_MAX;     // Minimum requirement.
@@ -132,10 +148,6 @@
     case _SC_THREAD_PRIO_INHERIT: return _POSIX_THREAD_PRIO_INHERIT;
     case _SC_THREAD_PRIO_PROTECT: return _POSIX_THREAD_PRIO_PROTECT;
     case _SC_THREAD_SAFE_FUNCTIONS:  return _POSIX_THREAD_SAFE_FUNCTIONS;
-    case _SC_NPROCESSORS_CONF:  return get_nprocs_conf();
-    case _SC_NPROCESSORS_ONLN:  return get_nprocs();
-    case _SC_PHYS_PAGES:        return get_phys_pages();
-    case _SC_AVPHYS_PAGES:      return get_avphys_pages();
     case _SC_MONOTONIC_CLOCK:   return _POSIX_VERSION;
 
     case _SC_2_PBS:             return -1;     // Obsolescent in POSIX.1-2008.