diff --git a/Demo/Podfile.lock b/Demo/Podfile.lock
index 60960d7..8eb7bb7 100644
--- a/Demo/Podfile.lock
+++ b/Demo/Podfile.lock
@@ -22,16 +22,16 @@ PODS:
     - AFNetworking/NSURLSession
   - librato-iOS (1.2.2):
     - AFNetworking (~> 2.0)
-    - Mantle (~> 1.3)
-  - Mantle (1.5.8):
-    - Mantle/extobjc (= 1.5.8)
-  - Mantle/extobjc (1.5.8)
+    - Mantle (~> 2.1)
+  - Mantle (2.1.0):
+    - Mantle/extobjc (= 2.1.0)
+  - Mantle/extobjc (2.1.0)
 
 DEPENDENCIES:
   - librato-iOS (from `../librato-iOS.podspec`)
 
 SPEC REPOS:
-  https://github.com/CocoaPods/Specs.git:
+  https://github.com/cocoapods/specs.git:
     - AFNetworking
     - Mantle
 
@@ -41,9 +41,9 @@ EXTERNAL SOURCES:
 
 SPEC CHECKSUMS:
   AFNetworking: cb8d14a848e831097108418f5d49217339d4eb60
-  librato-iOS: ac4f9b431c771cccc0719e8bdade35648fac507d
-  Mantle: f03b2b606c3f0cabd80214ad8a2fed6b464a7359
+  librato-iOS: e66bc97e62ef9aa7ca8b94ed318595c8b86cc81d
+  Mantle: 2fa750afa478cd625a94230fbf1c13462f29395b
 
 PODFILE CHECKSUM: 5817b13129eeec85d2fa75a097e506a23de0ee12
 
-COCOAPODS: 1.5.0
+COCOAPODS: 1.5.3
diff --git a/librato-iOS.podspec b/librato-iOS.podspec
index 2c99b2e..367ce76 100644
--- a/librato-iOS.podspec
+++ b/librato-iOS.podspec
@@ -18,5 +18,5 @@ Pod::Spec.new do |s|
     s.requires_arc          = true
 
     s.dependency 'AFNetworking', '~> 2.0'
-    s.dependency 'Mantle', '~> 1.3'
+    s.dependency 'Mantle', '~> 2.1'
 end
diff --git a/librato-iOS/Metrics/LibratoGaugeMetric.m b/librato-iOS/Metrics/LibratoGaugeMetric.m
index 16ee6df..5de2cbc 100644
--- a/librato-iOS/Metrics/LibratoGaugeMetric.m
+++ b/librato-iOS/Metrics/LibratoGaugeMetric.m
@@ -71,9 +71,7 @@ + (NSDictionary *)JSONKeyPathsByPropertyKey
         @"sum": sumKey,
         @"min": minKey,
         @"max": maxKey,
-        @"squares": squaresKey,
-        @"type": NSNull.null,
-        LibratoMetricValueKey: NSNull.null
+        @"squares": squaresKey
     };
 }
 
diff --git a/librato-iOS/Metrics/LibratoMetric.m b/librato-iOS/Metrics/LibratoMetric.m
index c5a2885..e7570d0 100644
--- a/librato-iOS/Metrics/LibratoMetric.m
+++ b/librato-iOS/Metrics/LibratoMetric.m
@@ -61,17 +61,16 @@ + (NSDictionary *)JSONKeyPathsByPropertyKey
         @"name": LibratoMetricNameKey,
         @"value": LibratoMetricValueKey,
         @"measureTime": LibratoMetricMeasureTimeKey,
-        @"source": LibratoMetricSourceKey,
-        @"type": NSNull.null
+        @"source": LibratoMetricSourceKey
     };
 }
 
 
 + (NSValueTransformer *)measureTimeJSONTransformer
 {
-    return [MTLValueTransformer reversibleTransformerWithForwardBlock:^id(NSNumber *epoch) {
+    return [MTLValueTransformer transformerUsingForwardBlock:^id(NSNumber *epoch, BOOL *success, NSError **error) {
         return [NSDate dateWithTimeIntervalSince1970:epoch.integerValue];
-    } reverseBlock:^id(NSDate *date) {
+    } reverseBlock:^id(NSDate *date, BOOL *success, NSError **error) {
         return @(floor(date.timeIntervalSince1970));
     }];
 }
@@ -79,10 +78,10 @@ + (NSValueTransformer *)measureTimeJSONTransformer
 
 + (NSValueTransformer *)nameJSONTransformer
 {
-    return [MTLValueTransformer reversibleTransformerWithForwardBlock:^id(NSString *name) {
+    return [MTLValueTransformer transformerUsingForwardBlock:^id(NSString *name, BOOL *success, NSError **error) {
         NSAssert(name.length > 0, @"Measurements must be named");
         return name.alm_sanitizedForMetric;
-    } reverseBlock:^id(NSString *name) {
+    } reverseBlock:^id(NSString *name, BOOL *success, NSError **error) {
         return name.alm_sanitizedForMetric;
     }];
 }
@@ -90,9 +89,9 @@ + (NSValueTransformer *)nameJSONTransformer
 
 + (NSValueTransformer *)sourceJSONTransformer
 {
-    return [MTLValueTransformer reversibleTransformerWithForwardBlock:^id(NSString *source) {
+    return [MTLValueTransformer transformerUsingForwardBlock:^id(NSString *source, BOOL *success, NSError **error) {
         return source.alm_sanitizedForMetric;
-    } reverseBlock:^id(NSString *source) {
+    } reverseBlock:^id(NSString *source, BOOL *success, NSError **error) {
         return (source.length ? source.alm_sanitizedForMetric : nil);
     }];
 }
@@ -100,10 +99,10 @@ + (NSValueTransformer *)sourceJSONTransformer
 
 + (NSValueTransformer *)valueJSONTransformer
 {
-    return [MTLValueTransformer reversibleTransformerWithForwardBlock:^id(NSNumber *value) {
+    return [MTLValueTransformer transformerUsingForwardBlock:^id(NSNumber *value, BOOL *success, NSError **error) {
         NSAssert([self.class isValidValue:value], @"Boolean is not a valid metric value");
         return value;
-    } reverseBlock:^id(NSNumber *value) {
+    } reverseBlock:^id(NSNumber *value, BOOL *success, NSError **error) {
         return value;
     }];
 }
@@ -113,7 +112,7 @@ + (NSValueTransformer *)valueJSONTransformer
 - (NSDictionary *)JSONDictionary
 {
     NSArray *nonNullableKeys = @[@"source"];
-	__block NSMutableDictionary *jsonDict = [MTLJSONAdapter JSONDictionaryFromModel:self].mutableCopy;
+    __block NSMutableDictionary *jsonDict = [MTLJSONAdapter JSONDictionaryFromModel:self error:nil].mutableCopy;
     [nonNullableKeys enumerateObjectsUsingBlock:^(NSString *key, NSUInteger idx, BOOL *stop) {
         if ([jsonDict.allKeys containsObject:key] && (jsonDict[key] == NSNull.null || jsonDict[key] == nil))
         {