diff --git a/Ably.xcodeproj/project.pbxproj b/Ably.xcodeproj/project.pbxproj
index 3bc202090..0b6981ca9 100644
--- a/Ably.xcodeproj/project.pbxproj
+++ b/Ably.xcodeproj/project.pbxproj
@@ -3923,6 +3923,7 @@
 				SWIFT_ACTIVE_COMPILATION_CONDITIONS = DEBUG;
 				SWIFT_OBJC_BRIDGING_HEADER = "Test/AblyTests-Bridging-Header.h";
 				SWIFT_OBJC_INTERFACE_HEADER_NAME = "Ably_Tests-Swift.h";
+				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_VERSION = 5.0;
 			};
 			name = Debug;
@@ -3989,6 +3990,7 @@
 				SWIFT_ACTIVE_COMPILATION_CONDITIONS = DEBUG;
 				SWIFT_OBJC_BRIDGING_HEADER = "Test/AblyTests-Bridging-Header.h";
 				SWIFT_OBJC_INTERFACE_HEADER_NAME = "Ably_Tests-Swift.h";
+				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_VERSION = 5.0;
 				TARGETED_DEVICE_FAMILY = 3;
 				TVOS_DEPLOYMENT_TARGET = 12.1;