diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index d5883950d..2f0b1b525 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -2661,7 +2661,7 @@ OPENSSL_EXPORT SSL_CTX *SSL_set_SSL_CTX(SSL *ssl, SSL_CTX *ctx);
 // WARNING: this function is dangerous because it breaks the usual return value
 // convention.
 OPENSSL_EXPORT int SSL_CTX_set_alpn_protos(SSL_CTX *ctx, const uint8_t *protos,
-                                           unsigned protos_len);
+                                           size_t protos_len);
 
 // SSL_set_alpn_protos sets the client ALPN protocol list on |ssl| to |protos|.
 // |protos| must be in wire-format (i.e. a series of non-empty, 8-bit
@@ -2671,7 +2671,7 @@ OPENSSL_EXPORT int SSL_CTX_set_alpn_protos(SSL_CTX *ctx, const uint8_t *protos,
 // WARNING: this function is dangerous because it breaks the usual return value
 // convention.
 OPENSSL_EXPORT int SSL_set_alpn_protos(SSL *ssl, const uint8_t *protos,
-                                       unsigned protos_len);
+                                       size_t protos_len);
 
 // SSL_CTX_set_alpn_select_cb sets a callback function on |ctx| that is called
 // during ClientHello processing in order to select an ALPN protocol from the
diff --git a/ssl/ssl_lib.cc b/ssl/ssl_lib.cc
index a3c25f3b7..313a0fa05 100644
--- a/ssl/ssl_lib.cc
+++ b/ssl/ssl_lib.cc
@@ -2149,14 +2149,14 @@ void SSL_CTX_set_next_proto_select_cb(
 }
 
 int SSL_CTX_set_alpn_protos(SSL_CTX *ctx, const uint8_t *protos,
-                            unsigned protos_len) {
+                            size_t protos_len) {
   // Note this function's calling convention is backwards.
   return ctx->alpn_client_proto_list.CopyFrom(MakeConstSpan(protos, protos_len))
              ? 0
              : 1;
 }
 
-int SSL_set_alpn_protos(SSL *ssl, const uint8_t *protos, unsigned protos_len) {
+int SSL_set_alpn_protos(SSL *ssl, const uint8_t *protos, size_t protos_len) {
   // Note this function's calling convention is backwards.
   if (!ssl->config) {
     return 1;