diff --git a/library/aes.c b/library/aes.c
index ef14671..267944a 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -1074,13 +1074,17 @@
                             const unsigned char *input,
                             unsigned char *output )
 {
+    int ret = 0;
     size_t n = *iv_off;
 
     while( length-- )
     {
         if( n == 0 )
-            mbedtls_aes_crypt_ecb( ctx, MBEDTLS_AES_ENCRYPT, iv, iv );
-
+        {
+            ret = mbedtls_aes_crypt_ecb( ctx, MBEDTLS_AES_ENCRYPT, iv, iv );
+            if( ret != 0 )
+                goto exit;
+        }
         *output++ =  *input++ ^ iv[n];
 
         n = ( n + 1 ) & 0x0F;
@@ -1088,7 +1092,8 @@
 
     *iv_off = n;
 
-    return( 0 );
+exit:
+    return( ret );
 }
 #endif /* MBEDTLS_CIPHER_MODE_OFB */
 
@@ -1247,6 +1252,72 @@
 };
 #endif /* MBEDTLS_CIPHER_MODE_CFB */
 
+#if defined(MBEDTLS_CIPHER_MODE_OFB)
+/*
+ * AES-OFB test vectors from:
+ *
+ * http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
+ */
+static const unsigned char aes_test_ofb_key[3][32] =
+{
+    { 0x2B, 0x7E, 0x15, 0x16, 0x28, 0xAE, 0xD2, 0xA6,
+      0xAB, 0xF7, 0x15, 0x88, 0x09, 0xCF, 0x4F, 0x3C },
+    { 0x8E, 0x73, 0xB0, 0xF7, 0xDA, 0x0E, 0x64, 0x52,
+      0xC8, 0x10, 0xF3, 0x2B, 0x80, 0x90, 0x79, 0xE5,
+      0x62, 0xF8, 0xEA, 0xD2, 0x52, 0x2C, 0x6B, 0x7B },
+    { 0x60, 0x3D, 0xEB, 0x10, 0x15, 0xCA, 0x71, 0xBE,
+      0x2B, 0x73, 0xAE, 0xF0, 0x85, 0x7D, 0x77, 0x81,
+      0x1F, 0x35, 0x2C, 0x07, 0x3B, 0x61, 0x08, 0xD7,
+      0x2D, 0x98, 0x10, 0xA3, 0x09, 0x14, 0xDF, 0xF4 }
+};
+
+static const unsigned char aes_test_ofb_iv[16] =
+{
+    0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+    0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F
+};
+
+static const unsigned char aes_test_ofb_pt[64] =
+{
+    0x6B, 0xC1, 0xBE, 0xE2, 0x2E, 0x40, 0x9F, 0x96,
+    0xE9, 0x3D, 0x7E, 0x11, 0x73, 0x93, 0x17, 0x2A,
+    0xAE, 0x2D, 0x8A, 0x57, 0x1E, 0x03, 0xAC, 0x9C,
+    0x9E, 0xB7, 0x6F, 0xAC, 0x45, 0xAF, 0x8E, 0x51,
+    0x30, 0xC8, 0x1C, 0x46, 0xA3, 0x5C, 0xE4, 0x11,
+    0xE5, 0xFB, 0xC1, 0x19, 0x1A, 0x0A, 0x52, 0xEF,
+    0xF6, 0x9F, 0x24, 0x45, 0xDF, 0x4F, 0x9B, 0x17,
+    0xAD, 0x2B, 0x41, 0x7B, 0xE6, 0x6C, 0x37, 0x10
+};
+
+static const unsigned char aes_test_ofb_ct[3][64] =
+{
+    { 0x3B, 0x3F, 0xD9, 0x2E, 0xB7, 0x2D, 0xAD, 0x20,
+      0x33, 0x34, 0x49, 0xF8, 0xE8, 0x3C, 0xFB, 0x4A,
+      0x77, 0x89, 0x50, 0x8d, 0x16, 0x91, 0x8f, 0x03,
+      0xf5, 0x3c, 0x52, 0xda, 0xc5, 0x4e, 0xd8, 0x25,
+      0x97, 0x40, 0x05, 0x1e, 0x9c, 0x5f, 0xec, 0xf6,
+      0x43, 0x44, 0xf7, 0xa8, 0x22, 0x60, 0xed, 0xcc,
+      0x30, 0x4c, 0x65, 0x28, 0xf6, 0x59, 0xc7, 0x78,
+      0x66, 0xa5, 0x10, 0xd9, 0xc1, 0xd6, 0xae, 0x5e },
+    { 0xCD, 0xC8, 0x0D, 0x6F, 0xDD, 0xF1, 0x8C, 0xAB,
+      0x34, 0xC2, 0x59, 0x09, 0xC9, 0x9A, 0x41, 0x74,
+      0xfc, 0xc2, 0x8b, 0x8d, 0x4c, 0x63, 0x83, 0x7c,
+      0x09, 0xe8, 0x17, 0x00, 0xc1, 0x10, 0x04, 0x01,
+      0x8d, 0x9a, 0x9a, 0xea, 0xc0, 0xf6, 0x59, 0x6f,
+      0x55, 0x9c, 0x6d, 0x4d, 0xaf, 0x59, 0xa5, 0xf2,
+      0x6d, 0x9f, 0x20, 0x08, 0x57, 0xca, 0x6c, 0x3e,
+      0x9c, 0xac, 0x52, 0x4b, 0xd9, 0xac, 0xc9, 0x2a },
+    { 0xDC, 0x7E, 0x84, 0xBF, 0xDA, 0x79, 0x16, 0x4B,
+      0x7E, 0xCD, 0x84, 0x86, 0x98, 0x5D, 0x38, 0x60,
+      0x4f, 0xeb, 0xdc, 0x67, 0x40, 0xd2, 0x0b, 0x3a,
+      0xc8, 0x8f, 0x6a, 0xd8, 0x2a, 0x4f, 0xb0, 0x8d,
+      0x71, 0xab, 0x47, 0xa0, 0x86, 0xe8, 0x6e, 0xed,
+      0xf3, 0x9d, 0x1c, 0x5b, 0xba, 0x97, 0xc4, 0x08,
+      0x01, 0x26, 0x14, 0x1d, 0x67, 0xf3, 0x7b, 0xe8,
+      0x53, 0x8f, 0x5a, 0x8b, 0xe7, 0x40, 0xe4, 0x84 }
+};
+#endif /* MBEDTLS_CIPHER_MODE_OFB */
+
 #if defined(MBEDTLS_CIPHER_MODE_CTR)
 /*
  * AES-CTR test vectors from:
@@ -1538,6 +1609,69 @@
         mbedtls_printf( "\n" );
 #endif /* MBEDTLS_CIPHER_MODE_CFB */
 
+#if defined(MBEDTLS_CIPHER_MODE_OFB)
+    /*
+     * OFB mode
+     */
+    for( i = 0; i < 6; i++ )
+    {
+        u = i >> 1;
+        keybits = 128 + u * 64;
+        mode = i & 1;
+
+        if( verbose != 0 )
+            mbedtls_printf( "  AES-OFB-%3d (%s): ", keybits,
+                            ( mode == MBEDTLS_AES_DECRYPT ) ? "dec" : "enc" );
+
+        memcpy( iv,  aes_test_ofb_iv, 16 );
+        memcpy( key, aes_test_ofb_key[u], keybits / 8 );
+
+        offset = 0;
+        ret = mbedtls_aes_setkey_enc( &ctx, key, keybits );
+        /*
+         * AES-192 is an optional feature that may be unavailable when
+         * there is an alternative underlying implementation i.e. when
+         * MBEDTLS_AES_ALT is defined.
+         */
+        if( ret == MBEDTLS_ERR_AES_FEATURE_UNAVAILABLE && keybits == 192 )
+        {
+            mbedtls_printf( "skipped\n" );
+            continue;
+        }
+        else if( ret != 0 )
+        {
+            goto exit;
+        }
+
+        if( mode == MBEDTLS_AES_DECRYPT )
+        {
+            memcpy( buf, aes_test_ofb_ct[u], 64 );
+            aes_tests = aes_test_ofb_pt;
+        }
+        else
+        {
+            memcpy( buf, aes_test_ofb_pt, 64 );
+            aes_tests = aes_test_ofb_ct[u];
+        }
+
+        ret = mbedtls_aes_crypt_ofb( &ctx, 64, &offset, iv, buf, buf );
+        if( ret != 0 )
+            goto exit;
+
+        if( memcmp( buf, aes_tests, 64 ) != 0 )
+        {
+            ret = 1;
+            goto exit;
+        }
+
+        if( verbose != 0 )
+            mbedtls_printf( "passed\n" );
+    }
+
+    if( verbose != 0 )
+        mbedtls_printf( "\n" );
+#endif /* MBEDTLS_CIPHER_MODE_OFB */
+
 #if defined(MBEDTLS_CIPHER_MODE_CTR)
     /*
      * CTR mode