diff --git a/include/mbedtls/pk.h b/include/mbedtls/pk.h
index 7d0f977..85e553a 100644
--- a/include/mbedtls/pk.h
+++ b/include/mbedtls/pk.h
@@ -760,7 +760,7 @@
  * \return          length of data written if successful, or a specific
  *                  error code
  */
-int mbedtls_pk_write_key_der( mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
+int mbedtls_pk_write_key_der( const mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
 
 /**
  * \brief           Write a public key to a SubjectPublicKeyInfo DER structure
@@ -775,7 +775,7 @@
  * \return          length of data written if successful, or a specific
  *                  error code
  */
-int mbedtls_pk_write_pubkey_der( mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
+int mbedtls_pk_write_pubkey_der( const mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
 
 #if defined(MBEDTLS_PEM_WRITE_C)
 /**
@@ -788,7 +788,7 @@
  *
  * \return          0 if successful, or a specific error code
  */
-int mbedtls_pk_write_pubkey_pem( mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
+int mbedtls_pk_write_pubkey_pem( const mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
 
 /**
  * \brief           Write a private key to a PKCS#1 or SEC1 PEM string
@@ -800,7 +800,7 @@
  *
  * \return          0 if successful, or a specific error code
  */
-int mbedtls_pk_write_key_pem( mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
+int mbedtls_pk_write_key_pem( const mbedtls_pk_context *ctx, unsigned char *buf, size_t size );
 #endif /* MBEDTLS_PEM_WRITE_C */
 #endif /* MBEDTLS_PK_WRITE_C */
 
diff --git a/library/pkwrite.c b/library/pkwrite.c
index 0da3698..4e6a082 100644
--- a/library/pkwrite.c
+++ b/library/pkwrite.c
@@ -222,7 +222,7 @@
     return( (int) len );
 }
 
-int mbedtls_pk_write_pubkey_der( mbedtls_pk_context *key, unsigned char *buf, size_t size )
+int mbedtls_pk_write_pubkey_der( const mbedtls_pk_context *key, unsigned char *buf, size_t size )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char *c;
@@ -310,7 +310,7 @@
     return( (int) len );
 }
 
-int mbedtls_pk_write_key_der( mbedtls_pk_context *key, unsigned char *buf, size_t size )
+int mbedtls_pk_write_key_der( const mbedtls_pk_context *key, unsigned char *buf, size_t size )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char *c;
@@ -553,7 +553,7 @@
 #define PRV_DER_MAX_BYTES   RSA_PRV_DER_MAX_BYTES > ECP_PRV_DER_MAX_BYTES ? \
                             RSA_PRV_DER_MAX_BYTES : ECP_PRV_DER_MAX_BYTES
 
-int mbedtls_pk_write_pubkey_pem( mbedtls_pk_context *key, unsigned char *buf, size_t size )
+int mbedtls_pk_write_pubkey_pem( const mbedtls_pk_context *key, unsigned char *buf, size_t size )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char output_buf[PUB_DER_MAX_BYTES];
@@ -578,7 +578,7 @@
     return( 0 );
 }
 
-int mbedtls_pk_write_key_pem( mbedtls_pk_context *key, unsigned char *buf, size_t size )
+int mbedtls_pk_write_key_pem( const mbedtls_pk_context *key, unsigned char *buf, size_t size )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned char output_buf[PRV_DER_MAX_BYTES];