diff --git a/lib/libmbedtls/sub.mk b/lib/libmbedtls/sub.mk
index 93d6df63e93..05951c0abd0 100644
--- a/lib/libmbedtls/sub.mk
+++ b/lib/libmbedtls/sub.mk
@@ -134,7 +134,7 @@ srcs-$(sm-$(ta-target)) += $(addprefix mbedtls/library/, $(SRCS_TLS))
 cflags-lib-y += -Wno-redundant-decls
 cflags-lib-y += -Wno-switch-default
 cflags-lib-y += -Wno-declaration-after-statement
-cflags-lib-y += -Wno-unused-functions
+cflags-lib-y += -Wno-unused-function
 
 ifeq ($(CFG_CRYPTOLIB_NAME_mbedtls),y)
 subdirs-$(sm-core) += core