--- a/config/external/nss/Makefile.in
+++ b/config/external/nss/Makefile.in
@@ -120,16 +120,17 @@ DEFAULT_GMAKE_FLAGS += CC='$(CC)'
 DEFAULT_GMAKE_FLAGS += SOURCE_MD_DIR=$(ABS_DIST)
 DEFAULT_GMAKE_FLAGS += SOURCE_MDHEADERS_DIR=$(NSPR_INCLUDE_DIR)
 DEFAULT_GMAKE_FLAGS += DIST=$(ABS_DIST)
 DEFAULT_GMAKE_FLAGS += NSPR_INCLUDE_DIR=$(NSPR_INCLUDE_DIR)
 DEFAULT_GMAKE_FLAGS += NSPR_LIB_DIR=$(NSPR_LIB_DIR)
 DEFAULT_GMAKE_FLAGS += MOZILLA_CLIENT=1
 DEFAULT_GMAKE_FLAGS += NO_MDUPDATE=1
 DEFAULT_GMAKE_FLAGS += NSS_ENABLE_ECC=1
+DEFAULT_GMAKE_FLAGS += NSS_ENABLE_TLS_1_3=1
 ifeq ($(OS_ARCH)_$(GNU_CC),WINNT_1)
 DEFAULT_GMAKE_FLAGS += OS_DLLFLAGS='-static-libgcc' NSPR31_LIB_PREFIX=lib
 endif
 ifndef MOZ_SYSTEM_SQLITE
 ifdef MOZ_FOLD_LIBS
 DEFAULT_GMAKE_FLAGS += SQLITE_LIB_NAME=nss3
 else
 DEFAULT_GMAKE_FLAGS += SQLITE_LIB_NAME=mozsqlite3