diff --git a/MasterPassword/C/mpw-algorithm.c b/MasterPassword/C/mpw-algorithm.c
index 89dbf422..c5620e30 100644
--- a/MasterPassword/C/mpw-algorithm.c
+++ b/MasterPassword/C/mpw-algorithm.c
@@ -19,6 +19,9 @@
 
 const uint8_t *mpw_masterKeyForUser(const char *fullName, const char *masterPassword, const MPAlgorithmVersion algorithmVersion) {
 
+    if (!fullName || !masterPassword)
+        return NULL;
+
     switch (algorithmVersion) {
         case MPAlgorithmVersion0:
             return mpw_masterKeyForUser_v0( fullName, masterPassword );
@@ -37,6 +40,9 @@ const uint8_t *mpw_masterKeyForUser(const char *fullName, const char *masterPass
 const char *mpw_passwordForSite(const uint8_t *masterKey, const char *siteName, const MPSiteType siteType, const uint32_t siteCounter,
         const MPSiteVariant siteVariant, const char *siteContext, const MPAlgorithmVersion algorithmVersion) {
 
+    if (!masterKey || !siteName)
+        return NULL;
+
     switch (algorithmVersion) {
         case MPAlgorithmVersion0:
             return mpw_passwordForSite_v0( masterKey, siteName, siteType, siteCounter, siteVariant, siteContext );
diff --git a/MasterPassword/ObjC/MPAppDelegate_Key.m b/MasterPassword/ObjC/MPAppDelegate_Key.m
index 9fd0af6f..b9903868 100644
--- a/MasterPassword/ObjC/MPAppDelegate_Key.m
+++ b/MasterPassword/ObjC/MPAppDelegate_Key.m
@@ -50,8 +50,8 @@ static NSDictionary *createKeyQuery(MPUserEntity *user, BOOL newItem, MPKeyOrigi
 
     return [PearlKeyChain createQueryForClass:kSecClassGenericPassword
                                    attributes:@{
-                                           (__bridge id)kSecAttrService    : @"Saved Master Password",
-                                           (__bridge id)kSecAttrAccount    : user.name?: @"",
+                                           (__bridge id)kSecAttrService : @"Saved Master Password",
+                                           (__bridge id)kSecAttrAccount : user.name?: @"",
 #if TARGET_OS_IPHONE
                                            (__bridge id)kSecAttrAccessible : (__bridge id)(kSecAttrAccessibleWhenPasscodeSetThisDeviceOnly?: kSecAttrAccessibleWhenUnlockedThisDeviceOnly),
 #endif
@@ -76,13 +76,14 @@ static NSDictionary *createKeyQuery(MPUserEntity *user, BOOL newItem, MPKeyOrigi
 - (void)storeSavedKeyFor:(MPUserEntity *)user {
 
     if (user.saveKey) {
-        inf( @"Saving key in keychain for user: %@", user.userID );
+        NSData *keyData = [self.key keyDataForAlgorithm:user.algorithm];
+        if (keyData) {
+            [self forgetSavedKeyFor:user];
 
-        [self forgetSavedKeyFor:user];
-        [PearlKeyChain addOrUpdateItemForQuery:createKeyQuery( user, YES, nil )
-                                withAttributes:@{
-                                        (__bridge id)kSecValueData : [self.key keyDataForAlgorithm:user.algorithm],
-                                }];
+            inf( @"Saving key in keychain for user: %@", user.userID );
+            [PearlKeyChain addOrUpdateItemForQuery:createKeyQuery( user, YES, nil )
+                                    withAttributes:@{ (__bridge id)kSecValueData : keyData }];
+        }
     }
 }
 
diff --git a/MasterPassword/ObjC/MPKey.m b/MasterPassword/ObjC/MPKey.m
index b34ef369..b482e5ec 100644
--- a/MasterPassword/ObjC/MPKey.m
+++ b/MasterPassword/ObjC/MPKey.m
@@ -62,9 +62,12 @@
 - (NSData *)keyDataForAlgorithm:(id<MPAlgorithm>)algorithm {
 
     NSData *keyData = [_keyCache objectForKey:algorithm];
-    if (!keyData)
-        [_keyCache setObject:keyData = [algorithm keyDataForFullName:self.fullName withMasterPassword:self.masterPassword]
-                      forKey:algorithm];
+    if (keyData)
+        return keyData;
+
+    keyData = [algorithm keyDataForFullName:self.fullName withMasterPassword:self.masterPassword];
+    if (keyData)
+        [_keyCache setObject:keyData forKey:algorithm];
 
     return keyData;
 }