diff --git a/MasterPassword/C/mpw-algorithm.c b/MasterPassword/C/mpw-algorithm.c
index dca0a0ea..9f6471c8 100644
--- a/MasterPassword/C/mpw-algorithm.c
+++ b/MasterPassword/C/mpw-algorithm.c
@@ -13,11 +13,11 @@
 
 #include "mpw-types.h"
 #include "mpw-util.h"
+#include "mpw-algorithm.h"
 
 #define MP_N                32768
 #define MP_r                8
 #define MP_p                2
-#define MP_dkLen            64
 #define MP_hash             PearlHashSHA256
 
 const uint8_t *mpw_masterKeyForUser(const char *fullName, const char *masterPassword) {
@@ -34,16 +34,20 @@ const uint8_t *mpw_masterKeyForUser(const char *fullName, const char *masterPass
     mpw_pushString( &masterKeySalt, &masterKeySaltSize, mpKeyScope );
     mpw_pushInt( &masterKeySalt, &masterKeySaltSize, htonl( strlen( fullName ) ) );
     mpw_pushString( &masterKeySalt, &masterKeySaltSize, fullName );
-    if (!masterKeySalt)
+    if (!masterKeySalt) {
         ftl( "Could not allocate master key salt: %d\n", errno );
+        return NULL;
+    }
     trc( "masterKeySalt ID: %s\n", mpw_idForBuf( masterKeySalt, masterKeySaltSize ) );
 
     // Calculate the master key.
     // masterKey = scrypt( masterPassword, masterKeySalt )
     const uint8_t *masterKey = mpw_scrypt( MP_dkLen, masterPassword, masterKeySalt, masterKeySaltSize, MP_N, MP_r, MP_p );
     mpw_free( masterKeySalt, masterKeySaltSize );
-    if (!masterKey)
+    if (!masterKey) {
         ftl( "Could not allocate master key: %d\n", errno );
+        return NULL;
+    }
     trc( "masterKey ID: %s\n", mpw_idForBuf( masterKey, MP_dkLen ) );
 
     return masterKey;
@@ -71,20 +75,28 @@ const char *mpw_passwordForSite(const uint8_t *masterKey, const char *siteName,
         mpw_pushInt( &sitePasswordInfo, &sitePasswordInfoSize, htonl( strlen( siteContext ) ) );
         mpw_pushString( &sitePasswordInfo, &sitePasswordInfoSize, siteContext );
     }
-    if (!sitePasswordInfo)
+    if (!sitePasswordInfo) {
         ftl( "Could not allocate site seed info: %d\n", errno );
+        return NULL;
+    }
     trc( "sitePasswordInfo ID: %s\n", mpw_idForBuf( sitePasswordInfo, sitePasswordInfoSize ) );
 
     const uint8_t *sitePasswordSeed = mpw_hmac_sha256( masterKey, MP_dkLen, sitePasswordInfo, sitePasswordInfoSize );
-    if (!sitePasswordSeed)
+    mpw_free( sitePasswordInfo, sitePasswordInfoSize );
+    if (!sitePasswordSeed) {
         ftl( "Could not allocate site seed: %d\n", errno );
+        return NULL;
+    }
     trc( "sitePasswordSeed ID: %s\n", mpw_idForBuf( sitePasswordSeed, 32 ) );
 
     // Determine the template.
     const char *template = mpw_templateForType( siteType, sitePasswordSeed[0] );
     trc( "type %d, template: %s\n", siteType, template );
-    if (strlen( template ) > 32)
+    if (strlen( template ) > 32) {
         ftl( "Template too long for password seed: %lu", strlen( template ) );
+        mpw_free( sitePasswordSeed, sizeof( sitePasswordSeed ) );
+        return NULL;
+    }
 
     // Encode the password from the seed using the template.
     char *const sitePassword = calloc( strlen( template ) + 1, sizeof( char ) );
diff --git a/MasterPassword/C/mpw-algorithm.h b/MasterPassword/C/mpw-algorithm.h
index 33f3ce93..ac080a93 100644
--- a/MasterPassword/C/mpw-algorithm.h
+++ b/MasterPassword/C/mpw-algorithm.h
@@ -6,13 +6,15 @@
 //  Copyright (c) 2014 Lyndir. All rights reserved.
 //
 
+#define MP_dkLen            64
+
 /** Derive the master key for a user based on their name and master password.
-  * @return A new 64-byte allocated buffer. */
+  * @return A new MP_dkLen-byte allocated buffer or NULL if an allocation error occurred. */
 const uint8_t *mpw_masterKeyForUser(
         const char *fullName, const char *masterPassword);
 
 /** Encode a password for the site from the given master key and site parameters.
-  * @return A newly allocated string. */
+  * @return A newly allocated string or NULL if an allocation error occurred. */
 const char *mpw_passwordForSite(
         const uint8_t *masterKey, const char *siteName, const MPSiteType siteType, const uint32_t siteCounter,
         const MPSiteVariant siteVariant, const char *siteContext);
diff --git a/MasterPassword/C/mpw-cli.c b/MasterPassword/C/mpw-cli.c
index b45c2ff1..0aee2a41 100644
--- a/MasterPassword/C/mpw-cli.c
+++ b/MasterPassword/C/mpw-cli.c
@@ -190,9 +190,14 @@ int main(int argc, char *const argv[]) {
     // Output the password.
     const uint8_t *masterKey = mpw_masterKeyForUser( fullName, masterPassword );
     mpw_free( masterPassword, strlen( masterPassword ) );
+    if (!masterKey)
+        ftl( "Couldn't derive master key." );
 
     const char *sitePassword = mpw_passwordForSite( masterKey, siteName, siteType, siteCounter, siteVariant, siteContextString );
-    fprintf( stdout, "%s\n", sitePassword );
+    mpw_free( masterKey, MP_dkLen );
+    if (!sitePassword)
+        ftl( "Couldn't derive site password." );
 
+    fprintf( stdout, "%s\n", sitePassword );
     return 0;
 }
diff --git a/MasterPassword/C/mpw-util.c b/MasterPassword/C/mpw-util.c
index cb9f0638..be7864c0 100644
--- a/MasterPassword/C/mpw-util.c
+++ b/MasterPassword/C/mpw-util.c
@@ -18,12 +18,16 @@
 void mpw_pushBuf(uint8_t **const buffer, size_t *const bufferSize, const void *pushBuffer, const size_t pushSize) {
 
     if (*bufferSize == (size_t)-1)
+        // The buffer was marked as broken, it is missing a previous push.  Abort to avoid corrupt content.
         return;
 
     *bufferSize += pushSize;
-    *buffer = realloc( *buffer, *bufferSize );
-    if (!*buffer) {
+    uint8_t **const resizedBuffer = realloc( *buffer, *bufferSize );
+    if (!resizedBuffer) {
+        // realloc failed, we can't push.  Mark the buffer as broken.
+        mpw_free( *buffer, *bufferSize - pushSize );
         *bufferSize = -1;
+        *buffer = NULL;
         return;
     }