diff --git a/phpseclib/Crypt/DES.php b/phpseclib/Crypt/DES.php
index 6a6d3389..e377c3a8 100644
--- a/phpseclib/Crypt/DES.php
+++ b/phpseclib/Crypt/DES.php
@@ -597,7 +597,7 @@ class Crypt_DES {
                 }
                 break;
             case CRYPT_DES_MODE_CFB:
-                if (!empty($buffer['xor'])) {
+                if (strlen($buffer['xor'])) {
                     $ciphertext = $plaintext ^ $buffer['xor'];
                     $iv = $buffer['encrypted'] . $ciphertext;
                     $start = strlen($ciphertext);
diff --git a/phpseclib/Crypt/Rijndael.php b/phpseclib/Crypt/Rijndael.php
index 71155c89..fec684a0 100644
--- a/phpseclib/Crypt/Rijndael.php
+++ b/phpseclib/Crypt/Rijndael.php
@@ -763,7 +763,7 @@ class Crypt_Rijndael {
                 }
                 break;
             case CRYPT_RIJNDAEL_MODE_CFB:
-                if (!empty($buffer['xor'])) {
+                if (strlen($buffer['xor'])) {
                     $ciphertext = $plaintext ^ $buffer['xor'];
                     $iv = $buffer['encrypted'] . $ciphertext;
                     $start = strlen($ciphertext);
diff --git a/phpseclib/Crypt/TripleDES.php b/phpseclib/Crypt/TripleDES.php
index faf8c18a..1e34acf3 100644
--- a/phpseclib/Crypt/TripleDES.php
+++ b/phpseclib/Crypt/TripleDES.php
@@ -617,7 +617,7 @@ class Crypt_TripleDES {
                 }
                 break;
             case CRYPT_DES_MODE_CFB:
-                if (!empty($buffer['xor'])) {
+                if (strlen($buffer['xor'])) {
                     $ciphertext = $plaintext ^ $buffer['xor'];
                     $iv = $buffer['encrypted'] . $ciphertext;
                     $start = strlen($ciphertext);
diff --git a/phpseclib/Math/BigInteger.php b/phpseclib/Math/BigInteger.php
index 04bcdf40..d048cb03 100644
--- a/phpseclib/Math/BigInteger.php
+++ b/phpseclib/Math/BigInteger.php
@@ -302,7 +302,7 @@ class Math_BigInteger {
         }
 
         // '0' counts as empty() but when the base is 256 '0' is equal to ord('0') or 48
-        // '0' is the only  value like this per http://php.net/empty
+        // '0' is the only value like this per http://php.net/empty
         if (empty($x) && (abs($base) != 256 || $x !== '0')) {
             return;
         }