diff --git a/CleanroomConcurrency.xcodeproj/project.pbxproj b/CleanroomConcurrency.xcodeproj/project.pbxproj
index ad82c3f..3000840 100644
--- a/CleanroomConcurrency.xcodeproj/project.pbxproj
+++ b/CleanroomConcurrency.xcodeproj/project.pbxproj
@@ -352,6 +352,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
+				MACOSX_DEPLOYMENT_TARGET = 10.9;
 				MTL_ENABLE_DEBUG_INFO = YES;
 				ONLY_ACTIVE_ARCH = YES;
 				SWIFT_ACTIVE_COMPILATION_CONDITIONS = DEBUG;
@@ -403,6 +404,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
+				MACOSX_DEPLOYMENT_TARGET = 10.9;
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
 				VALIDATE_PRODUCT = YES;
@@ -420,6 +422,7 @@
 				DYLIB_CURRENT_VERSION = 21;
 				DYLIB_INSTALL_NAME_BASE = "@rpath";
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
+				MACOSX_DEPLOYMENT_TARGET = 10.9;
 				SKIP_INSTALL = YES;
 				SWIFT_VERSION = 4.0;
 			};
@@ -434,6 +437,7 @@
 				DYLIB_CURRENT_VERSION = 21;
 				DYLIB_INSTALL_NAME_BASE = "@rpath";
 				INSTALL_PATH = "$(LOCAL_LIBRARY_DIR)/Frameworks";
+				MACOSX_DEPLOYMENT_TARGET = 10.9;
 				SKIP_INSTALL = YES;
 				SWIFT_VERSION = 4.0;
 			};