diff --git a/bip39-standalone.html b/bip39-standalone.html
index 43b588a..6be3415 100644
--- a/bip39-standalone.html
+++ b/bip39-standalone.html
@@ -39133,10 +39133,11 @@ var Mnemonic = function(language) {
 
     self.toSeed = function(mnemonic, passphrase) {
         passphrase = passphrase || '';
-        mnemonic = self.joinWords(self.splitWords(self.normalizeString(mnemonic))); // removes blanks
+        mnemonic = self.joinWords(self.splitWords(mnemonic)); // removes duplicate blanks
+        var mnemonicNormalized = self.normalizeString(mnemonic);
         passphrase = self.normalizeString(passphrase)
         passphrase = "mnemonic" + passphrase;
-        var mnemonicBits = sjcl.codec.utf8String.toBits(mnemonic);
+        var mnemonicBits = sjcl.codec.utf8String.toBits(mnemonicNormalized);
         var passphraseBits = sjcl.codec.utf8String.toBits(passphrase);
         var result = sjcl.misc.pbkdf2(mnemonicBits, passphraseBits, PBKDF2_ROUNDS, 512, hmacSHA512);
         var hashHex = sjcl.codec.hex.fromBits(result);
diff --git a/src/js/jsbip39.js b/src/js/jsbip39.js
index 67ba5a7..025f625 100644
--- a/src/js/jsbip39.js
+++ b/src/js/jsbip39.js
@@ -130,10 +130,11 @@ var Mnemonic = function(language) {
 
     self.toSeed = function(mnemonic, passphrase) {
         passphrase = passphrase || '';
-        mnemonic = self.joinWords(self.splitWords(self.normalizeString(mnemonic))); // removes blanks
+        mnemonic = self.joinWords(self.splitWords(mnemonic)); // removes duplicate blanks
+        var mnemonicNormalized = self.normalizeString(mnemonic);
         passphrase = self.normalizeString(passphrase)
         passphrase = "mnemonic" + passphrase;
-        var mnemonicBits = sjcl.codec.utf8String.toBits(mnemonic);
+        var mnemonicBits = sjcl.codec.utf8String.toBits(mnemonicNormalized);
         var passphraseBits = sjcl.codec.utf8String.toBits(passphrase);
         var result = sjcl.misc.pbkdf2(mnemonicBits, passphraseBits, PBKDF2_ROUNDS, 512, hmacSHA512);
         var hashHex = sjcl.codec.hex.fromBits(result);