diff --git a/libc/bionic/fortify.cpp b/libc/bionic/fortify.cpp
index 20e265e..cf37666 100644
--- a/libc/bionic/fortify.cpp
+++ b/libc/bionic/fortify.cpp
@@ -500,3 +500,10 @@
   return memcpy(dst, src, count);
 }
 #endif // NO___MEMCPY_CHK
+
+// Runtime implementation of __mempcpy_chk (used directly by compiler, not in headers).
+extern "C" void* __mempcpy_chk(void* dst, const void* src, size_t count, size_t dst_len) {
+  __check_count("mempcpy", "count", count);
+  __check_buffer_access("mempcpy", "write into", count, dst_len);
+  return mempcpy(dst, src, count);
+}
diff --git a/libc/include/bits/fortify/string.h b/libc/include/bits/fortify/string.h
index 0e205d3..70e4476 100644
--- a/libc/include/bits/fortify/string.h
+++ b/libc/include/bits/fortify/string.h
@@ -66,6 +66,22 @@
 }
 #endif /* __ANDROID_API__ >= __ANDROID_API_J_MR1__ */
 
+#if defined(__USE_GNU)
+#if __ANDROID_API__ >= __ANDROID_API_R__
+__BIONIC_FORTIFY_INLINE
+void* mempcpy(void* const dst __pass_object_size0, const void* src, size_t copy_amount)
+        __overloadable
+        __clang_error_if(__bos_unevaluated_lt(__bos0(dst), copy_amount),
+                         "'mempcpy' called with size bigger than buffer") {
+    size_t bos_dst = __bos0(dst);
+    if (__bos_trivially_not_lt(bos_dst, copy_amount)) {
+        return __builtin_mempcpy(dst, src, copy_amount);
+    }
+    return __builtin___mempcpy_chk(dst, src, copy_amount, bos_dst);
+}
+#endif /* __ANDROID_API__ >= __ANDROID_API_R__ */
+#endif
+
 #if __ANDROID_API__ >= __ANDROID_API_L__
 __BIONIC_FORTIFY_INLINE
 char* stpcpy(char* const dst __pass_object_size, const char* src)
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index b12df56..3c23da2 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1482,6 +1482,7 @@
 
 LIBC_R { # introduced=R
   global:
+    __mempcpy_chk;
     __open64_2;
     __openat64_2;
     call_once;