diff --git a/libc/bionic/dlmalloc.h b/libc/bionic/dlmalloc.h
index b34165e..a00a583 100644
--- a/libc/bionic/dlmalloc.h
+++ b/libc/bionic/dlmalloc.h
@@ -24,6 +24,7 @@
 #define REALLOC_ZERO_BYTES_FREES 1
 #define USE_DL_PREFIX 1
 #define USE_LOCKS 1
+#define LOCK_AT_FORK 1
 #define USE_RECURSIVE_LOCK 0
 #define USE_SPIN_LOCKS 0