diff --git a/utils/swift_build_support/swift_build_support/products/earlyswiftsyntax.py b/utils/swift_build_support/swift_build_support/products/earlyswiftsyntax.py
index 4bcce9e09bbb9..485be3c1a497d 100644
--- a/utils/swift_build_support/swift_build_support/products/earlyswiftsyntax.py
+++ b/utils/swift_build_support/swift_build_support/products/earlyswiftsyntax.py
@@ -54,6 +54,8 @@ def build(self, host_target):
         self.generate_toolchain_file_for_darwin_or_linux(host_target)
 
         self.cmake_options.define('CMAKE_INSTALL_PREFIX:PATH', self.args.install_prefix)
+        self.cmake_options.define('SWIFTSYNTAX_ENABLE_ASSERTIONS:BOOL',
+                                  self.args.assertions)
         self.build_with_cmake(["all"], self.args.swift_build_variant, [])
 
     def should_test(self, host_target):