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.
diff --git a/libc/kernel/tools/defaults.py b/libc/kernel/tools/defaults.py
index 773d22f..340af13 100644
--- a/libc/kernel/tools/defaults.py
+++ b/libc/kernel/tools/defaults.py
@@ -53,9 +53,10 @@
     "x86": {},
     }
 
-# Replace tokens in the output according to this mapping
+# Replace tokens in the output according to this mapping.
 kernel_token_replacements = {
-    "asm": "__asm__",
+    # The kernel's ARG_MAX is actually the "minimum" maximum (see fs/exec.c).
+    "ARG_MAX": "_KERNEL_ARG_MAX",
     # The kernel usage of __unused for unused struct fields conflicts with the macro defined in <sys/cdefs.h>.
     "__unused": "__linux_unused",
     # The kernel's _NSIG/NSIG are one less than the userspace value, so we need to move them aside.
diff --git a/libc/kernel/uapi/linux/limits.h b/libc/kernel/uapi/linux/limits.h
index 406d175..4441592 100644
--- a/libc/kernel/uapi/linux/limits.h
+++ b/libc/kernel/uapi/linux/limits.h
@@ -21,7 +21,7 @@
 #define NR_OPEN 1024
 #define NGROUPS_MAX 65536
 /* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
-#define ARG_MAX 131072
+#define _KERNEL_ARG_MAX 131072
 #define LINK_MAX 127
 #define MAX_CANON 255
 #define MAX_INPUT 255
diff --git a/tests/unistd_test.cpp b/tests/unistd_test.cpp
index 3a87e88..32b1626 100644
--- a/tests/unistd_test.cpp
+++ b/tests/unistd_test.cpp
@@ -857,6 +857,39 @@
   ASSERT_EQ(online_cpus, sysconf(_SC_NPROCESSORS_ONLN));
 }
 
+TEST(UNISTD_TEST, sysconf_SC_ARG_MAX) {
+  // Since Linux 2.6.23, ARG_MAX isn't a constant and depends on RLIMIT_STACK.
+
+  // Get our current limit, and set things up so we restore the limit.
+  rlimit rl;
+  ASSERT_EQ(0, getrlimit(RLIMIT_STACK, &rl));
+  uint64_t original_rlim_cur = rl.rlim_cur;
+  if (rl.rlim_cur == RLIM_INFINITY) {
+    rl.rlim_cur = 8 * 1024 * 1024; // Bionic reports unlimited stacks as 8MiB.
+  }
+  auto guard = make_scope_guard([&rl, original_rlim_cur]() {
+    rl.rlim_cur = original_rlim_cur;
+    ASSERT_EQ(0, setrlimit(RLIMIT_STACK, &rl));
+  });
+
+  // _SC_ARG_MAX should be 1/4 the stack size.
+  EXPECT_EQ(static_cast<long>(rl.rlim_cur / 4), sysconf(_SC_ARG_MAX));
+
+  // If you have a really small stack, the kernel still guarantees "32 pages" (fs/exec.c).
+  rl.rlim_cur = 1024;
+  rl.rlim_max = RLIM_INFINITY;
+  ASSERT_EQ(0, setrlimit(RLIMIT_STACK, &rl));
+
+  EXPECT_EQ(static_cast<long>(32 * sysconf(_SC_PAGE_SIZE)), sysconf(_SC_ARG_MAX));
+
+  // With a 128-page stack limit, we know exactly what _SC_ARG_MAX should be...
+  rl.rlim_cur = 128 * sysconf(_SC_PAGE_SIZE);
+  rl.rlim_max = RLIM_INFINITY;
+  ASSERT_EQ(0, setrlimit(RLIMIT_STACK, &rl));
+
+  EXPECT_EQ(static_cast<long>((128 * sysconf(_SC_PAGE_SIZE)) / 4), sysconf(_SC_ARG_MAX));
+}
+
 TEST(UNISTD_TEST, dup2_same) {
   // POSIX says of dup2:
   // If fildes2 is already a valid open file descriptor ...