diff --git a/meta-arm/recipes-security/optee/optee-os/missing-mkdir.patch b/meta-arm/recipes-security/optee/optee-os/missing-mkdir.patch
new file mode 100644
index 00000000..db1b47f8
--- /dev/null
+++ b/meta-arm/recipes-security/optee/optee-os/missing-mkdir.patch
@@ -0,0 +1,31 @@
+Upstream-Status: Backport [https://github.com/OP-TEE/optee_os/pull/4000]
+Signed-off-by: Ross Burton <ross.burton@arm.com>
+
+From 79384a244d1972cdb02114f5cde6fcaf2e014c9b Mon Sep 17 00:00:00 2001
+From: Jerome Forissier <jerome@forissier.org>
+Date: Tue, 28 Jul 2020 17:28:43 +0200
+Subject: [PATCH] build: fix race when generating conf.mk
+
+This patch fixes the following error triggered by a heavily parallel build:
+
+ echo sm := ta_arm64 > .../export-ta_arm64/mk/conf.mk.tmp
+ /bin/bash: .../export-ta_arm64/mk/conf.mk.tmp: No such file or directory
+
+Fixes: https://github.com/OP-TEE/optee_os/issues/3999
+Signed-off-by: Jerome Forissier <jerome@forissier.org>
+---
+ ta/ta.mk | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/ta/ta.mk b/ta/ta.mk
+index 59ed87f71d..ad97edaf08 100644
+--- a/ta/ta.mk
++++ b/ta/ta.mk
+@@ -190,6 +190,7 @@ define mk-file-export
+ .PHONY: $(conf-mk-file-export)
+ $(conf-mk-file-export):
+ 	@$$(cmd-echo-silent) '  CHK    ' $$@
++	$(q)mkdir -p $$(dir $$@)
+ 	$(q)echo sm := $$(sm-$(conf-mk-file-export)) > $$@.tmp
+ 	$(q)echo sm-$$(sm-$(conf-mk-file-export)) := y >> $$@.tmp
+ 	$(q)($$(foreach v, $$(ta-mk-file-export-vars-$$(sm-$(conf-mk-file-export))), \
diff --git a/meta-arm/recipes-security/optee/optee-os_git.bb b/meta-arm/recipes-security/optee/optee-os_git.bb
index 52c11558..deeb5158 100644
--- a/meta-arm/recipes-security/optee/optee-os_git.bb
+++ b/meta-arm/recipes-security/optee/optee-os_git.bb
@@ -21,6 +21,7 @@ SRC_URI = " \
     file://0004-Cleanup-unused-comp-cflags-sm-from-libgcc-lookup-com.patch \
     file://0005-Fixup-Allow-use-of-cc-option-in-core-arch-arm-arm.mk.patch \
     file://0006-allow-setting-sysroot-for-libgcc-lookup.patch \
+    file://missing-mkdir.patch \
 "
 
 S = "${WORKDIR}/git"