diff --git a/programs/x509/cert_req.c b/programs/x509/cert_req.c
index dcfd176..72d59b5 100644
--- a/programs/x509/cert_req.c
+++ b/programs/x509/cert_req.c
@@ -107,7 +107,7 @@
     mbedtls_md_type_t md_alg;         /* Hash algorithm used for signature.   */
 } opt;
 
-int write_certificate_request(mbedtls_x509write_csr *req, const char *output_file,
+static int write_certificate_request(mbedtls_x509write_csr *req, const char *output_file,
                               int (*f_rng)(void *, unsigned char *, size_t),
                               void *p_rng)
 {
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;
diff --git a/programs/x509/load_roots.c b/programs/x509/load_roots.c
index f0e6acf..d14537f 100644
--- a/programs/x509/load_roots.c
+++ b/programs/x509/load_roots.c
@@ -48,7 +48,7 @@
 } opt;
 
 
-int read_certificates(const char *const *filenames)
+static int read_certificates(const char *const *filenames)
 {
     mbedtls_x509_crt cas;
     int ret = 0;