diff --git a/programs/x509/cert_write.c b/programs/x509/cert_write.c
index 0b2575e..1aa1d0f 100644
--- a/programs/x509/cert_write.c
+++ b/programs/x509/cert_write.c
@@ -204,7 +204,7 @@
     int format;                 /* format                               */
 } opt;
 
-int write_certificate(mbedtls_x509write_cert *crt, const char *output_file,
+static int write_certificate(mbedtls_x509write_cert *crt, const char *output_file,
                       int (*f_rng)(void *, unsigned char *, size_t),
                       void *p_rng)
 {
@@ -249,7 +249,7 @@
     return 0;
 }
 
-int parse_serial_decimal_format(unsigned char *obuf, size_t obufmax,
+static int parse_serial_decimal_format(unsigned char *obuf, size_t obufmax,
                                 const char *ibuf, size_t *len)
 {
     unsigned long long int dec;