diff --git a/library/debug.c b/library/debug.c
index a032478..a9cd814 100644
--- a/library/debug.c
+++ b/library/debug.c
@@ -86,7 +86,7 @@
     char str[DEBUG_BUF_SIZE];
     int ret;
 
-    if( ssl->conf == NULL || ssl->conf->f_dbg == NULL || level > debug_threshold )
+    if( NULL == ssl || NULL == ssl->conf || NULL == ssl->conf->f_dbg || level > debug_threshold )
         return;
 
     va_start( argp, format );
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 9208ec9..80a908d 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -5773,7 +5773,7 @@
 {
     mbedtls_ecjpake_role role;
 
-    if( ssl->handshake == NULL && ssl->conf == NULL )
+    if( ssl->handshake == NULL || ssl->conf == NULL )
         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
 
     if( ssl->conf->endpoint == MBEDTLS_SSL_IS_SERVER )
diff --git a/programs/aes/crypt_and_hash.c b/programs/aes/crypt_and_hash.c
index 102144e..a14d20c 100644
--- a/programs/aes/crypt_and_hash.c
+++ b/programs/aes/crypt_and_hash.c
@@ -184,7 +184,12 @@
         mbedtls_fprintf( stderr, "Message Digest '%s' not found\n", argv[5] );
         goto exit;
     }
-    mbedtls_md_setup( &md_ctx, md_info, 1 );
+
+    if( mbedtls_md_setup( &md_ctx, md_info, 1 ) != 0 )
+    {
+        mbedtls_fprintf( stderr, "mbedtls_md_setup failed\n" );
+        goto exit;
+    }
 
     /*
      * Read the secret key and clean the command line.
@@ -399,6 +404,15 @@
             goto exit;
         }
 
+        if( mbedtls_cipher_get_block_size( &cipher_ctx ) == 0 )
+        {
+            mbedtls_fprintf( stderr, "Invalid cipher block size: 0. \n" );
+            goto exit;
+        }
+
+        /*
+         * Check the file size.
+         */
         if( ( ( filesize - mbedtls_md_get_size( md_info ) ) %
                 mbedtls_cipher_get_block_size( &cipher_ctx ) ) != 0 )
         {