diff --git a/lib/vtls/vtls.c b/lib/vtls/vtls.c
index 82883c9c55..fe43703bf8 100644
--- a/lib/vtls/vtls.c
+++ b/lib/vtls/vtls.c
@@ -497,7 +497,7 @@ void Curl_ssl_delsessionid(struct Curl_easy *data, void *ssl_sessionid)
  */
 CURLcode Curl_ssl_addsessionid(struct Curl_easy *data,
                                struct connectdata *conn,
-                               bool isProxy,
+                               const bool isProxy,
                                void *ssl_sessionid,
                                size_t idsize,
                                int sockindex)
diff --git a/lib/vtls/vtls.h b/lib/vtls/vtls.h
index a0585c9cec..f1a9b8033a 100644
--- a/lib/vtls/vtls.h
+++ b/lib/vtls/vtls.h
@@ -247,7 +247,7 @@ void Curl_ssl_sessionid_unlock(struct Curl_easy *data);
  */
 bool Curl_ssl_getsessionid(struct Curl_easy *data,
                            struct connectdata *conn,
-                           const bool isproxy,
+                           const bool isProxy,
                            void **ssl_sessionid,
                            size_t *idsize, /* set 0 if unknown */
                            int sockindex);