diff --git a/meta-arm/recipes-security/optee/optee.inc b/meta-arm/recipes-security/optee/optee.inc
index af391f39..1569a9df 100644
--- a/meta-arm/recipes-security/optee/optee.inc
+++ b/meta-arm/recipes-security/optee/optee.inc
@@ -15,6 +15,9 @@ OPTEE_ARCH:arm = "arm32"
 OPTEE_ARCH:aarch64 = "arm64"
 OPTEE_CORE = "${@d.getVar('OPTEE_ARCH').upper()}"
 
+# FIXME - breaks with Clang 18.  See https://github.com/OP-TEE/optee_os/issues/6754
+TOOLCHAIN = "gcc"
+
 OPTEE_TOOLCHAIN = "${@d.getVar('TOOLCHAIN') or 'gcc'}"
 OPTEE_COMPILER = "${@bb.utils.contains("BBFILE_COLLECTIONS", "clang-layer", "${OPTEE_TOOLCHAIN}", "gcc", d)}"