diff --git a/phpseclib/Crypt/DES.php b/phpseclib/Crypt/DES.php
index e377c3a8..8b857c6c 100644
--- a/phpseclib/Crypt/DES.php
+++ b/phpseclib/Crypt/DES.php
@@ -774,7 +774,7 @@ class Crypt_DES {
                 }
                 break;
             case CRYPT_DES_MODE_CFB:
-                if (!empty($buffer['ciphertext'])) {
+                if (strlen($buffer['ciphertext'])) {
                     $plaintext = $ciphertext ^ substr($this->decryptIV, strlen($buffer['ciphertext']));
                     $buffer['ciphertext'].= substr($ciphertext, 0, strlen($plaintext));
                     if (strlen($buffer['ciphertext']) == 8) {
diff --git a/phpseclib/Crypt/Rijndael.php b/phpseclib/Crypt/Rijndael.php
index fec684a0..dc22488b 100644
--- a/phpseclib/Crypt/Rijndael.php
+++ b/phpseclib/Crypt/Rijndael.php
@@ -741,7 +741,7 @@ class Crypt_Rijndael {
                 break;
             case CRYPT_RIJNDAEL_MODE_CTR:
                 $xor = $this->encryptIV;
-                if (!empty($buffer['encrypted'])) {
+                if (strlen($buffer['encrypted'])) {
                     for ($i = 0; $i < strlen($plaintext); $i+=$block_size) {
                         $block = substr($plaintext, $i, $block_size);
                         $buffer['encrypted'].= $this->_encryptBlock($this->_generate_xor($block_size, $xor));
@@ -862,7 +862,7 @@ class Crypt_Rijndael {
                 break;
             case CRYPT_RIJNDAEL_MODE_CTR:
                 $xor = $this->decryptIV;
-                if (!empty($buffer['ciphertext'])) {
+                if (strlen($buffer['ciphertext'])) {
                     for ($i = 0; $i < strlen($ciphertext); $i+=$block_size) {
                         $block = substr($ciphertext, $i, $block_size);
                         $buffer['ciphertext'].= $this->_encryptBlock($this->_generate_xor($block_size, $xor));
@@ -884,7 +884,7 @@ class Crypt_Rijndael {
                 }
                 break;
             case CRYPT_RIJNDAEL_MODE_CFB:
-                if (!empty($buffer['ciphertext'])) {
+                if (strlen($buffer['ciphertext'])) {
                     $plaintext = $ciphertext ^ substr($this->decryptIV, strlen($buffer['ciphertext']));
                     $buffer['ciphertext'].= substr($ciphertext, 0, strlen($plaintext));
                     if (strlen($buffer['ciphertext']) == $block_size) {
diff --git a/phpseclib/Crypt/TripleDES.php b/phpseclib/Crypt/TripleDES.php
index 1e34acf3..f92f7c34 100644
--- a/phpseclib/Crypt/TripleDES.php
+++ b/phpseclib/Crypt/TripleDES.php
@@ -822,7 +822,7 @@ class Crypt_TripleDES {
                 }
                 break;
             case CRYPT_DES_MODE_CFB:
-                if (!empty($buffer['ciphertext'])) {
+                if (strlen($buffer['ciphertext'])) {
                     $plaintext = $ciphertext ^ substr($this->decryptIV, strlen($buffer['ciphertext']));
                     $buffer['ciphertext'].= substr($ciphertext, 0, strlen($plaintext));
                     if (strlen($buffer['ciphertext']) == 8) {