diff --git a/libc/private/bionic_tls.h b/libc/private/bionic_tls.h
index da34344..82c8cd9 100644
--- a/libc/private/bionic_tls.h
+++ b/libc/private/bionic_tls.h
@@ -60,6 +60,13 @@
 #define TLS_SLOT_OPENGL_API         3
 #define TLS_SLOT_OPENGL             4
 
+/* this slot is only used to pass information from the dynamic linker to
+ * libc.so when the C library is loaded in to memory. The C runtime init
+ * function will then clear it. Since its use is extremely temporary,
+ * we reuse an existing location.
+ */
+#define  TLS_SLOT_BIONIC_PREINIT    (TLS_SLOT_ERRNO+1)
+
 /* small technical note: it is not possible to call pthread_setspecific
  * on keys that are <= TLS_SLOT_MAX_WELL_KNOWN, which is why it is set to
  * TLS_SLOT_ERRNO.