diff --git a/Sources/GATTClient.swift b/Sources/GATTClient.swift
index b95735ef5..7f0785e0c 100755
--- a/Sources/GATTClient.swift
+++ b/Sources/GATTClient.swift
@@ -1057,7 +1057,7 @@ public final class GATTClient {
                 // write next part
                 let maxLength = Int(connection.maximumTransmissionUnit.rawValue) - ATTPrepareWriteRequest.length // 5
                 let endIndex = min(offset + maxLength, operation.data.count)
-                let attributeValuePart = operation.data.subdata(in: offset ..< endIndex)
+                let attributeValuePart = operation.data.subdataNoCopy(in: offset ..< endIndex)
                 
                 let pdu = ATTPrepareWriteRequest(handle: operation.lastRequest.handle,
                                                  offset: UInt16(offset),
diff --git a/Sources/GATTServer.swift b/Sources/GATTServer.swift
index 007ea192b..3d8f6dec0 100644
--- a/Sources/GATTServer.swift
+++ b/Sources/GATTServer.swift
@@ -884,6 +884,7 @@ internal extension GATTDatabase {
         let handleRange = handle.end < UInt16.max ? Range(handle.start ... handle.end) : Range(handle.start ..< handle.end)
         
         var data: [(start: UInt16, end: UInt16, uuid: BluetoothUUID)] = []
+        data.reserveCapacity(attributeGroups.count)
         
         for group in attributeGroups {
             
@@ -893,7 +894,7 @@ internal extension GATTDatabase {
             
             guard groupRange.isSubset(handleRange) else { continue }
             
-            let serviceUUID = BluetoothUUID(littleEndian: BluetoothUUID(data: Data(group.serviceAttribute.value))!)
+            let serviceUUID = BluetoothUUID(littleEndian: BluetoothUUID(data: group.serviceAttribute.value)!)
             
             data.append((group.startHandle, group.endHandle, serviceUUID))
         }