diff --git a/simpleble/src/backends/macos/PeripheralBaseMacOS.mm b/simpleble/src/backends/macos/PeripheralBaseMacOS.mm
index a4262fd7..29902039 100644
--- a/simpleble/src/backends/macos/PeripheralBaseMacOS.mm
+++ b/simpleble/src/backends/macos/PeripheralBaseMacOS.mm
@@ -213,12 +213,13 @@ - (void)connect {
                 for (CBDescriptor* descriptor in characteristic.descriptors) {
                     @synchronized(self) {
                         [characteristicExtras.descriptorExtras setObject:[[DescriptorExtras alloc] init]
-                                                                  forKey:[[descriptor.UUID UUIDString] lowercaseString]];
+                                                                  forKey:uuidToString(descriptor.UUID)];
                     }
                 }
 
                 @synchronized(self) {
-                    [self.characteristicExtras setObject:characteristicExtras forKey:[[characteristic.UUID UUIDString] lowercaseString]];
+                    NSLog(@"Characteristic %@ loaded", [characteristic.UUID UUIDString]);
+                    [self.characteristicExtras setObject:characteristicExtras forKey:uuidToString(characteristic.UUID)];
                 }
             }
         }
@@ -627,7 +628,8 @@ - (void)peripheral:(CBPeripheral*)peripheral
 }
 
 - (void)peripheral:(CBPeripheral*)peripheral didUpdateValueForCharacteristic:(CBCharacteristic*)characteristic error:(NSError*)error {
-    CharacteristicExtras* characteristicExtras = [self.characteristicExtras objectForKey:[[characteristic.UUID UUIDString] lowercaseString]];
+    NSLog(@"Characteristic %@ updated", [characteristic.UUID UUIDString]);
+    CharacteristicExtras* characteristicExtras = [self.characteristicExtras objectForKey:uuidToString(characteristic.UUID)];
 
     if (characteristic.isNotifying) {
         // If the characteristic is notifying, just save the value and trigger the callback.
@@ -651,7 +653,7 @@ - (void)peripheral:(CBPeripheral*)peripheral didUpdateValueForCharacteristic:(CB
 }
 
 - (void)peripheral:(CBPeripheral*)peripheral didWriteValueForCharacteristic:(CBCharacteristic*)characteristic error:(NSError*)error {
-    CharacteristicExtras* characteristicExtras = [self.characteristicExtras objectForKey:[[characteristic.UUID UUIDString] lowercaseString]];
+    CharacteristicExtras* characteristicExtras = [self.characteristicExtras objectForKey:uuidToString(characteristic.UUID)];
     BleTask* task = characteristicExtras.task;
 
     @synchronized(self) {
@@ -663,7 +665,7 @@ - (void)peripheral:(CBPeripheral*)peripheral didWriteValueForCharacteristic:(CBC
 - (void)peripheral:(CBPeripheral*)peripheral
     didUpdateNotificationStateForCharacteristic:(CBCharacteristic*)characteristic
                                           error:(NSError*)error {
-    CharacteristicExtras* characteristicExtras = [self.characteristicExtras objectForKey:[[characteristic.UUID UUIDString] lowercaseString]];
+    CharacteristicExtras* characteristicExtras = [self.characteristicExtras objectForKey:uuidToString(characteristic.UUID)];
     BleTask* task = characteristicExtras.task;
 
     @synchronized(self) {
@@ -677,8 +679,8 @@ - (void)peripheralIsReadyToSendWriteWithoutResponse:(CBPeripheral*)peripheral {
 }
 
 - (void)peripheral:(CBPeripheral*)peripheral didUpdateValueForDescriptor:(CBDescriptor*)descriptor error:(NSError*)error {
-    CharacteristicExtras* characteristicExtras = [self.characteristicExtras objectForKey:[[descriptor.characteristic.UUID UUIDString] lowercaseString]];
-    DescriptorExtras* descriptorExtras = [characteristicExtras.descriptorExtras objectForKey:[[descriptor.UUID UUIDString] lowercaseString]];
+    CharacteristicExtras* characteristicExtras = [self.characteristicExtras objectForKey:uuidToString(descriptor.characteristic.UUID)];
+    DescriptorExtras* descriptorExtras = [characteristicExtras.descriptorExtras objectForKey:uuidToString(descriptor.UUID)];
     BleTask* task = descriptorExtras.task;
 
     @synchronized(self) {
@@ -688,8 +690,8 @@ - (void)peripheral:(CBPeripheral*)peripheral didUpdateValueForDescriptor:(CBDesc
 }
 
 - (void)peripheral:(CBPeripheral*)peripheral didWriteValueForDescriptor:(CBDescriptor*)descriptor error:(NSError*)error {
-    CharacteristicExtras* characteristicExtras = [self.characteristicExtras objectForKey:[[descriptor.characteristic.UUID UUIDString] lowercaseString]];
-    DescriptorExtras* descriptorExtras = [characteristicExtras.descriptorExtras objectForKey:[[descriptor.UUID UUIDString] lowercaseString]];
+    CharacteristicExtras* characteristicExtras = [self.characteristicExtras objectForKey:uuidToString(descriptor.characteristic.UUID)];
+    DescriptorExtras* descriptorExtras = [characteristicExtras.descriptorExtras objectForKey:uuidToString(descriptor.UUID)];
     BleTask* task = descriptorExtras.task;
 
     @synchronized(self) {
diff --git a/simpleble/src/backends/macos/Utils.h b/simpleble/src/backends/macos/Utils.h
index 2773cd77..65c49caf 100644
--- a/simpleble/src/backends/macos/Utils.h
+++ b/simpleble/src/backends/macos/Utils.h
@@ -6,3 +6,4 @@
 #include <simpleble/Types.h>
 
 SimpleBLE::BluetoothUUID uuidToSimpleBLE(CBUUID* uuid);
+NSString* uuidToString(CBUUID* uuid);
diff --git a/simpleble/src/backends/macos/Utils.mm b/simpleble/src/backends/macos/Utils.mm
index 90485f18..d6ceb182 100644
--- a/simpleble/src/backends/macos/Utils.mm
+++ b/simpleble/src/backends/macos/Utils.mm
@@ -11,3 +11,13 @@
         return uuid_raw;
     }
 }
+
+NSString* uuidToString(CBUUID* uuid) {
+    NSString* uuidString = [[uuid UUIDString] lowercaseString];
+
+    if ([uuidString length] == 4) {
+        return [NSString stringWithFormat:@"0000%@-0000-1000-8000-00805f9b34fb", uuidString];
+    } else {
+        return uuidString;
+    }
+}