diff --git a/chat.h b/chat.h
index f47b244..829dd1d 100644
--- a/chat.h
+++ b/chat.h
@@ -239,3 +239,6 @@ static inline void base64(char *dst, const byte *src, size_t len) {
 
 // Defined in libcrypto if missing from libc:
 void explicit_bzero(void *b, size_t len);
+#ifndef strlcat
+size_t strlcat(char *restrict dst, const char *restrict src, size_t dstsize);
+#endif