diff --git a/libc/bionic/brk.cpp b/libc/bionic/brk.cpp
index 4e46193..a8c078b 100644
--- a/libc/bionic/brk.cpp
+++ b/libc/bionic/brk.cpp
@@ -35,6 +35,8 @@
 void* __bionic_brk; // Accidentally exported by the NDK.
 #endif
 
+extern "C" void* __brk(void* __addr);
+
 int brk(void* end_data) {
   __bionic_brk = __brk(end_data);
   if (__bionic_brk < end_data) {