diff --git a/library/x509_create.c b/library/x509_create.c
index 1639630..88148a6 100644
--- a/library/x509_create.c
+++ b/library/x509_create.c
@@ -126,7 +126,7 @@
     return( cur );
 }
 
-int mbedtls_x509_string_to_names( mbedtls_asn1_named_data **head, const char *name )
+static int mbedtls_x509_string_to_names( mbedtls_asn1_named_data **head, const char *name )
 {
     int ret = 0;
     const char *s = name, *c = s;
@@ -211,7 +211,7 @@
 /* The first byte of the value in the mbedtls_asn1_named_data structure is reserved
  * to store the critical boolean for us
  */
-int mbedtls_x509_set_extension( mbedtls_asn1_named_data **head, const char *oid, size_t oid_len,
+static int mbedtls_x509_set_extension( mbedtls_asn1_named_data **head, const char *oid, size_t oid_len,
                         int critical, const unsigned char *val, size_t val_len )
 {
     mbedtls_asn1_named_data *cur;
@@ -292,7 +292,7 @@
     return( (int) len );
 }
 
-int mbedtls_x509_write_sig( unsigned char **p, unsigned char *start,
+static int mbedtls_x509_write_sig( unsigned char **p, unsigned char *start,
                     const char *oid, size_t oid_len,
                     unsigned char *sig, size_t size )
 {
@@ -361,7 +361,7 @@
  *                 -- by extnID
  *     }
  */
-int mbedtls_x509_write_extensions( unsigned char **p, unsigned char *start,
+static int mbedtls_x509_write_extensions( unsigned char **p, unsigned char *start,
                            mbedtls_asn1_named_data *first )
 {
     int ret;