diff --git a/ChangeLog b/ChangeLog
index 3469445e9..f03b83d09 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -5,6 +5,7 @@ mbed TLS ChangeLog (Sorted per branch, date)
 Bugfix
    * Allow loading symlinked certificates. Fixes #3005. Reported and fixed
      by Jonathan Bennett <JBennett@incomsystems.biz> via #3008.
+   * Fix an unchecked call to mbedtls_md() in the x509write module.
 
 Security
    * Fix potential memory overread when performing an ECDSA signature
@@ -14,6 +15,8 @@ Security
      denial of service (application crash or extra resource consumption).
      Found by Auke Zeilstra and Peter Schwabe, using static analysis.
 
+Bugfix
+
 = mbed TLS 2.16.4 branch released 2020-01-15
 
 Security
diff --git a/library/cipher.c b/library/cipher.c
index 273997577..8d010b59a 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -361,6 +361,10 @@ int mbedtls_cipher_update( mbedtls_cipher_context_t *ctx, const unsigned char *i
 
     *olen = 0;
     block_size = mbedtls_cipher_get_block_size( ctx );
+    if ( 0 == block_size )
+    {
+        return( MBEDTLS_ERR_CIPHER_INVALID_CONTEXT );
+    }
 
     if( ctx->cipher_info->mode == MBEDTLS_MODE_ECB )
     {
@@ -396,11 +400,6 @@ int mbedtls_cipher_update( mbedtls_cipher_context_t *ctx, const unsigned char *i
     }
 #endif
 
-    if ( 0 == block_size )
-    {
-        return( MBEDTLS_ERR_CIPHER_INVALID_CONTEXT );
-    }
-
     if( input == output &&
        ( ctx->unprocessed_len != 0 || ilen % block_size ) )
     {
@@ -459,11 +458,6 @@ int mbedtls_cipher_update( mbedtls_cipher_context_t *ctx, const unsigned char *i
          */
         if( 0 != ilen )
         {
-            if( 0 == block_size )
-            {
-                return( MBEDTLS_ERR_CIPHER_INVALID_CONTEXT );
-            }
-
             /* Encryption: only cache partial blocks
              * Decryption w/ padding: always keep at least one whole block
              * Decryption w/o padding: only cache partial blocks
diff --git a/library/x509write_csr.c b/library/x509write_csr.c
index b65a11c6a..7406a9754 100644
--- a/library/x509write_csr.c
+++ b/library/x509write_csr.c
@@ -226,7 +226,9 @@ int mbedtls_x509write_csr_der( mbedtls_x509write_csr *ctx, unsigned char *buf, s
     /*
      * Prepare signature
      */
-    mbedtls_md( mbedtls_md_info_from_type( ctx->md_alg ), c, len, hash );
+    ret = mbedtls_md( mbedtls_md_info_from_type( ctx->md_alg ), c, len, hash );
+    if( ret != 0 )
+        return( ret );
 
     if( ( ret = mbedtls_pk_sign( ctx->key, ctx->md_alg, hash, 0, sig, &sig_len,
                                  f_rng, p_rng ) ) != 0 )
diff --git a/tests/suites/test_suite_ecdsa.function b/tests/suites/test_suite_ecdsa.function
index 0e7283bc7..2844beaa5 100644
--- a/tests/suites/test_suite_ecdsa.function
+++ b/tests/suites/test_suite_ecdsa.function
@@ -527,7 +527,9 @@ void ecdsa_write_restart( int id, char *d_str, int md_alg,
     TEST_ASSERT( md_info != NULL );
 
     hlen = mbedtls_md_get_size( md_info );
-    mbedtls_md( md_info, (const unsigned char *) msg, strlen( msg ), hash );
+    TEST_ASSERT( mbedtls_md( md_info,
+                             (const unsigned char *) msg, strlen( msg ),
+                             hash ) == 0 );
 
     mbedtls_ecp_set_max_ops( max_ops );
 
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index 97c338b85..bebca5a0a 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -550,8 +550,8 @@ void mbedtls_mpi_lt_mpi_ct( int size_X, char * input_X,
     TEST_ASSERT( mbedtls_mpi_read_string( &X, 16, input_X ) == 0 );
     TEST_ASSERT( mbedtls_mpi_read_string( &Y, 16, input_Y ) == 0 );
 
-    mbedtls_mpi_grow( &X, size_X );
-    mbedtls_mpi_grow( &Y, size_Y );
+    TEST_ASSERT( mbedtls_mpi_grow( &X, size_X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_grow( &Y, size_Y ) == 0 );
 
     TEST_ASSERT( mbedtls_mpi_lt_mpi_ct( &X, &Y, &ret ) == input_err );
     if( input_err == 0 )
diff --git a/tests/suites/test_suite_pk.function b/tests/suites/test_suite_pk.function
index 342405e5d..b57fe19fa 100644
--- a/tests/suites/test_suite_pk.function
+++ b/tests/suites/test_suite_pk.function
@@ -712,7 +712,9 @@ void pk_sign_verify_restart( int pk_type, int grp_id, char *d_str,
     TEST_ASSERT( md_info != NULL );
 
     hlen = mbedtls_md_get_size( md_info );
-    mbedtls_md( md_info, (const unsigned char *) msg, strlen( msg ), hash );
+    TEST_ASSERT( mbedtls_md( md_info,
+                             (const unsigned char *) msg, strlen( msg ),
+                             hash ) == 0 );
 
     mbedtls_ecp_set_max_ops( max_ops );