diff --git a/deployments/psa-api-test/initial_attestation/iat-api-test.cmake b/deployments/psa-api-test/initial_attestation/iat-api-test.cmake
index 55ecd4a..5486075 100644
--- a/deployments/psa-api-test/initial_attestation/iat-api-test.cmake
+++ b/deployments/psa-api-test/initial_attestation/iat-api-test.cmake
@@ -14,9 +14,8 @@
 #-------------------------------------------------------------------------------
 #  Set additional defines needed for build.
 #-------------------------------------------------------------------------------
-set(TS_ARCH_TEST_EXTERNAL_DEFS
-	-DPSA_ALG_MD4=0x02000002
-	CACHE STRING "Arch test external defines")
+list(APPEND PSA_ARCH_TEST_EXTERNAL_DEFS
+	-DPSA_ALG_MD4=0x02000002)
 
 #-------------------------------------------------------------------------------
 #  The arch test build system puts its build output under a test suite specific