diff --git a/Makefile b/Makefile
index 57ed37c1c..b02682a54 100644
--- a/Makefile
+++ b/Makefile
@@ -60,7 +60,7 @@
 #   build/config.mk
 
 SHELL      = build/bootstrap/cocmd.com
-HOSTS     ?= freebsd openbsd netbsd rhel7 rhel5 win10 xnu
+HOSTS     ?= freebsd openbsd netbsd rhel7 rhel5 xnu win10 win10:31338
 MAKEFLAGS += -j --no-builtin-rules
 
 .SUFFIXES:
diff --git a/libc/calls/ntcontext2linux.c b/libc/calls/ntcontext2linux.c
index 8d527ee9e..818682d9e 100644
--- a/libc/calls/ntcontext2linux.c
+++ b/libc/calls/ntcontext2linux.c
@@ -23,7 +23,6 @@
 
 privileged void _ntcontext2linux(ucontext_t *ctx, const struct NtContext *cr) {
   if (!cr) return;
-  ctx->uc_flags = cr->EFlags;
   ctx->uc_mcontext.eflags = cr->EFlags;
   ctx->uc_mcontext.rax = cr->Rax;
   ctx->uc_mcontext.rbx = cr->Rbx;
@@ -51,7 +50,6 @@ privileged void _ntcontext2linux(ucontext_t *ctx, const struct NtContext *cr) {
 
 privileged void _ntlinux2context(struct NtContext *cr, const ucontext_t *ctx) {
   if (!cr) return;
-  cr->EFlags = ctx->uc_flags;
   cr->EFlags = ctx->uc_mcontext.eflags;
   cr->Rax = ctx->uc_mcontext.rax;
   cr->Rbx = ctx->uc_mcontext.rbx;
diff --git a/libc/calls/sigenter-freebsd.c b/libc/calls/sigenter-freebsd.c
index 8e22c94ff..c4d3c4d14 100644
--- a/libc/calls/sigenter-freebsd.c
+++ b/libc/calls/sigenter-freebsd.c
@@ -51,7 +51,6 @@ privileged void __sigenter_freebsd(int sig, struct siginfo_freebsd *freebsdinfo,
       g.uc.uc_stack.ss_sp = ctx->uc_stack.ss_sp;
       g.uc.uc_stack.ss_size = ctx->uc_stack.ss_size;
       g.uc.uc_stack.ss_flags = ctx->uc_stack.ss_flags;
-      g.uc.uc_flags = ctx->uc_flags;
       __repmovsb(&g.uc.uc_sigmask, &ctx->uc_sigmask,
                  MIN(sizeof(g.uc.uc_sigmask), sizeof(ctx->uc_sigmask)));
       g.uc.uc_mcontext.r8 = ctx->uc_mcontext.mc_r8;
diff --git a/libc/calls/sigenter-netbsd.c b/libc/calls/sigenter-netbsd.c
index 41b75eccf..585076c43 100644
--- a/libc/calls/sigenter-netbsd.c
+++ b/libc/calls/sigenter-netbsd.c
@@ -47,7 +47,6 @@ privileged void __sigenter_netbsd(int sig, struct siginfo_netbsd *si,
       __repstosb(&uc, 0, sizeof(uc));
       __siginfo2cosmo(&si2, (void *)si);
       uc.uc_mcontext.fpregs = &uc.__fpustate;
-      uc.uc_flags = ctx->uc_flags;
       uc.uc_stack.ss_sp = ctx->uc_stack.ss_sp;
       uc.uc_stack.ss_size = ctx->uc_stack.ss_size;
       uc.uc_stack.ss_flags = ctx->uc_stack.ss_flags;
diff --git a/libc/calls/sigenter-xnu.c b/libc/calls/sigenter-xnu.c
index 89e9381e8..80ff59d89 100644
--- a/libc/calls/sigenter-xnu.c
+++ b/libc/calls/sigenter-xnu.c
@@ -471,7 +471,6 @@ privileged void __sigenter_xnu(void *fn, int infostyle, int sig,
     } else {
       __repstosb(&g, 0, sizeof(g));
       if (xnuctx) {
-        g.uc.uc_flags = xnuctx->uc_onstack ? SA_ONSTACK : 0;
         g.uc.uc_sigmask.__bits[0] = xnuctx->uc_sigmask;
         g.uc.uc_sigmask.__bits[1] = 0;
         g.uc.uc_stack.ss_sp = xnuctx->uc_stack.ss_sp;
diff --git a/libc/calls/ucontext.h b/libc/calls/ucontext.h
index 05be425fd..6540d1852 100644
--- a/libc/calls/ucontext.h
+++ b/libc/calls/ucontext.h
@@ -72,7 +72,7 @@ struct MachineContext {
 typedef struct MachineContext mcontext_t;
 
 struct ucontext {
-  uint64_t uc_flags;
+  uint64_t uc_flags; /* don't use this */
   struct ucontext *uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext; /* use this */
diff --git a/test/libc/calls/sigaction_test.c b/test/libc/calls/sigaction_test.c
index 6a78cc085..f45c57124 100644
--- a/test/libc/calls/sigaction_test.c
+++ b/test/libc/calls/sigaction_test.c
@@ -25,9 +25,11 @@
 #include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/nexgen32e/nexgen32e.h"
+#include "libc/runtime/internal.h"
 #include "libc/runtime/runtime.h"
 #include "libc/sysv/consts/sa.h"
 #include "libc/sysv/consts/sig.h"
+#include "libc/sysv/consts/uc.h"
 #include "libc/testlib/testlib.h"
 #include "third_party/xed/x86.h"
 
@@ -196,6 +198,8 @@ TEST(sigaction, autoZombieSlayer) {
   // verify it works
   ASSERT_NE(-1, (pid = fork()));
   if (!pid) _Exit(0);
+  // XXX: WSL does the wrong thing here.
+  if (__is_wsl()) usleep(10);
   ASSERT_SYS(ECHILD, -1, wait(0));
   // clean up
   ASSERT_SYS(0, 0, sigaction(SIGCHLD, &sa, 0));
diff --git a/test/libc/log/backtrace_test.c b/test/libc/log/backtrace_test.c
index aa46bfe62..b0aebad48 100644
--- a/test/libc/log/backtrace_test.c
+++ b/test/libc/log/backtrace_test.c
@@ -325,10 +325,13 @@ TEST(ShowCrashReports, testDivideByZero) {
               _gc(IndentLines(output, -1, 0, 4)));
       __die();
     }
-    if (!strstr(output, "3.141")) {
-      fprintf(stderr, "ERROR: crash report didn't have fpu register\n%s\n",
-              _gc(IndentLines(output, -1, 0, 4)));
-      __die();
+    // XXX: WSL doesn't save and restore x87 registers to ucontext_t
+    if (!__is_wsl()) {
+      if (!strstr(output, "3.141")) {
+        fprintf(stderr, "ERROR: crash report didn't have fpu register\n%s\n",
+                _gc(IndentLines(output, -1, 0, 4)));
+        __die();
+      }
     }
     if (!strstr(output, "0f0e0d0c0b0a09080706050403020100")) {
       fprintf(stderr, "ERROR: crash report didn't have sse register\n%s\n",