diff --git a/libc/bionic/legacy_32_bit_support.cpp b/libc/bionic/legacy_32_bit_support.cpp
index 4e19ebf..e66126b 100644
--- a/libc/bionic/legacy_32_bit_support.cpp
+++ b/libc/bionic/legacy_32_bit_support.cpp
@@ -161,3 +161,9 @@
   }
   return __mremap(old_address, old_size, new_size, flags, new_address);
 }
+
+// mseal(2) is LP64-only.
+int mseal(void*, size_t, unsigned long) {
+  errno = ENOSYS;
+  return -1;
+}