diff --git a/src/http.c b/src/http.c
index eeadfede..3d0a7b35 100644
--- a/src/http.c
+++ b/src/http.c
@@ -498,7 +498,7 @@ static size_t oidc_http_response_header(char *buffer, size_t size, size_t nitems
 		while (*value == ' ')
 			value++;
 		/* remove trailing /r/n */
-		i = strlen(value) - 1;
+		i = _oidc_strlen(value) - 1;
 		while ((value[i] == '\r') || (value[i] == '\n'))
 			value[i--] = '\0';
 	}
@@ -810,7 +810,7 @@ static apr_byte_t oidc_http_request(request_rec *r, const char *url, const char
 	}
 
 	if (dpop != NULL) {
-		oidc_debug(r, "appending DPoP header (len=%d)", (int)strlen(dpop));
+		oidc_debug(r, "appending DPoP header (len=%d)", (int)_oidc_strlen(dpop));
 		h_list = curl_slist_append(h_list, apr_psprintf(r->pool, "%s: %s", OIDC_HTTP_HDR_DPOP, dpop));
 	}
 
diff --git a/src/proto/dpop.c b/src/proto/dpop.c
index a473f38a..3085c8f5 100644
--- a/src/proto/dpop.c
+++ b/src/proto/dpop.c
@@ -104,7 +104,7 @@ apr_byte_t oidc_proto_dpop_create(request_rec *r, oidc_cfg_t *cfg, const char *u
 
 	if (access_token != NULL) {
 		if (oidc_jose_hash_and_base64url_encode(r->pool, OIDC_JOSE_ALG_SHA256, access_token,
-							strlen(access_token), &ath, &err) == FALSE) {
+							_oidc_strlen(access_token), &ath, &err) == FALSE) {
 			oidc_error(r, "oidc_jose_hash_and_base64url_encode failed: %s", oidc_jose_e2s(r->pool, err));
 			goto end;
 		}