diff --git a/include/mbedtls/sha512.h b/include/mbedtls/sha512.h
index 93f9646..bf40e4b 100644
--- a/include/mbedtls/sha512.h
+++ b/include/mbedtls/sha512.h
@@ -116,8 +116,7 @@
  *                 and have a hash operation started.
  * \param input    The buffer holding the input data. This must
  *                 be a readable buffer of length \p ilen Bytes.
- *                 It must not be \c NULL.
- * \param ilen     The length of the input data \p input in Bytes.
+ * \param ilen     The length of the input data in Bytes.
  *
  * \return         \c 0 on success.
  * \return         A negative error code on failure.
@@ -184,8 +183,8 @@
  * \param ctx      The SHA-512 context. This must be initialized
  *                 and have a hash operation started.
  * \param input    The buffer holding the data. This must be a readable
- *                 buffer of length \p ilen Bytes. It must not be \c NULL.
- * \param ilen     The length of the input data \p input in Bytes.
+ *                 buffer of length \p ilen Bytes.
+ * \param ilen     The length of the input data in Bytes.
  */
 MBEDTLS_DEPRECATED void mbedtls_sha512_update( mbedtls_sha512_context *ctx,
                                                const unsigned char *input,
@@ -235,9 +234,8 @@
  *                 output = SHA-512(input buffer).
  *
  * \param input    The buffer holding the input data. This must be
- *                 a readable buffer of length \p ilen Bytes. It
- *                 must not be \c NULL.
- * \param ilen     The length of the input data \p input in Bytes.
+ *                 a readable buffer of length \p ilen Bytes.
+ * \param ilen     The length of the input data in Bytes.
  * \param output   The SHA-384 or SHA-512 checksum result.
  *                 This must be a writable buffer of length \c 64 Bytes.
  * \param is384    Determines which function to use. This must be either
@@ -270,9 +268,8 @@
  * \deprecated     Superseded by mbedtls_sha512_ret() in 2.7.0
  *
  * \param input    The buffer holding the data. This must be a
- *                 readable buffer of length \p ilen Bytes. It
- *                 must not be \c NULL.
- * \param ilen     The length of the input data \p input in Bytes.
+ *                 readable buffer of length \p ilen Bytes.
+ * \param ilen     The length of the input data in Bytes.
  * \param output   The SHA-384 or SHA-512 checksum result. This must
  *                 be a writable buffer of length \c 64 Bytes.
  * \param is384    Determines which function to use. This must be eiher
diff --git a/library/sha512.c b/library/sha512.c
index 7a99170..8260f32 100644
--- a/library/sha512.c
+++ b/library/sha512.c
@@ -89,8 +89,8 @@
 #endif /* PUT_UINT64_BE */
 
 #define MBEDTLS_SHA512_VALIDATE_RET(cond)                           \
-    MBEDTLS_VALIDATE_RET( MBEDTLS_ERR_SHA512_BAD_INPUT_DATA, cond )
-#define MBEDTLS_SHA512_VALIDATE(cond)               MBEDTLS_VALIDATE( cond )
+    MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_SHA512_BAD_INPUT_DATA )
+#define MBEDTLS_SHA512_VALIDATE(cond)  MBEDTLS_INTERNAL_VALIDATE( cond )
 
 void mbedtls_sha512_init( mbedtls_sha512_context *ctx )
 {
@@ -122,6 +122,7 @@
 int mbedtls_sha512_starts_ret( mbedtls_sha512_context *ctx, int is384 )
 {
     MBEDTLS_SHA512_VALIDATE_RET( ctx != NULL );
+    MBEDTLS_SHA512_VALIDATE_RET( is384 == 0 || is384 == 1 );
 
     ctx->total[0] = 0;
     ctx->total[1] = 0;
@@ -308,12 +309,12 @@
     size_t fill;
     unsigned int left;
 
+    MBEDTLS_SHA512_VALIDATE_RET( ctx != NULL );
+    MBEDTLS_SHA512_VALIDATE_RET( ilen == 0 || input != NULL );
+
     if( ilen == 0 )
         return( 0 );
 
-    MBEDTLS_SHA512_VALIDATE_RET( ctx != NULL );
-    MBEDTLS_SHA512_VALIDATE_RET( input != NULL );
-
     left = (unsigned int) (ctx->total[0] & 0x7F);
     fill = 128 - left;
 
@@ -447,6 +448,7 @@
     int ret;
     mbedtls_sha512_context ctx;
 
+    MBEDTLS_SHA512_VALIDATE_RET( is384 == 0 || is384 == 1 );
     MBEDTLS_SHA512_VALIDATE_RET( ilen == 0 || input != NULL );
     MBEDTLS_SHA512_VALIDATE_RET( (unsigned char *)output != NULL );