diff --git a/libc/include/sys/ucontext.h b/libc/include/sys/ucontext.h
index 4cc66eb..730ac69 100644
--- a/libc/include/sys/ucontext.h
+++ b/libc/include/sys/ucontext.h
@@ -87,9 +87,14 @@
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
-  sigset_t uc_sigmask;
-  /* Android has a wrong (smaller) sigset_t on ARM. */
-  uint32_t __padding_rt_sigset;
+  union {
+    struct {
+      sigset_t uc_sigmask;
+      /* Android has a wrong (smaller) sigset_t on ARM. */
+      uint32_t __padding_rt_sigset;
+    };
+    sigset64_t uc_sigmask64;
+  };
   /* The kernel adds extra padding after uc_sigmask to match glibc sigset_t on ARM. */
   char __padding[120];
   unsigned long uc_regspace[128] __attribute__((__aligned__(8)));
@@ -109,7 +114,10 @@
   unsigned long uc_flags;
   struct ucontext *uc_link;
   stack_t uc_stack;
-  sigset_t uc_sigmask;
+  union {
+    sigset_t uc_sigmask;
+    sigset64_t uc_sigmask64;
+  };
   /* The kernel adds extra padding after uc_sigmask to match glibc sigset_t on ARM64. */
   char __padding[128 - sizeof(sigset_t)];
   mcontext_t uc_mcontext;
@@ -194,9 +202,14 @@
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
-  sigset_t uc_sigmask;
-  /* Android has a wrong (smaller) sigset_t on x86. */
-  uint32_t __padding_rt_sigset;
+  union {
+    struct {
+      sigset_t uc_sigmask;
+      /* Android has a wrong (smaller) sigset_t on x86. */
+      uint32_t __padding_rt_sigset;
+    };
+    sigset64_t uc_sigmask64;
+  };
   struct _libc_fpstate __fpregs_mem;
 } ucontext_t;
 
@@ -266,7 +279,10 @@
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
-  sigset_t uc_sigmask;
+  union {
+    sigset_t uc_sigmask;
+    sigset64_t uc_sigmask64;
+  };
 } ucontext_t;
 
 #elif defined(__x86_64__)
@@ -362,7 +378,10 @@
   struct ucontext* uc_link;
   stack_t uc_stack;
   mcontext_t uc_mcontext;
-  sigset_t uc_sigmask;
+  union {
+    sigset_t uc_sigmask;
+    sigset64_t uc_sigmask64;
+  };
   struct _libc_fpstate __fpregs_mem;
 } ucontext_t;