diff --git a/crypto/bio/internal.h b/crypto/bio/internal.h
index dd3d800..ba28839 100644
--- a/crypto/bio/internal.h
+++ b/crypto/bio/internal.h
@@ -92,7 +92,7 @@
 /* BIO_clear_socket_error clears the last system socket error.
  *
  * TODO(fork): remove all callers of this. */
-void bio_clear_socket_error();
+void bio_clear_socket_error(void);
 
 /* BIO_sock_error returns the last socket error on |sock|. */
 int bio_sock_error(int sock);