diff --git a/.gitmodules b/.gitmodules
index f88af6f..fabee45 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -17,7 +17,7 @@
 [submodule "mbedtls"]
 	path = third_party/mbedtls/repo
 	url = https://github.com/ARMmbed/mbedtls.git
-	branch = mbedtls-2.18
+	branch = mbedtls-2.25
 [submodule "qrcode"]
 	path = examples/common/QRCode/repo
 	url = https://github.com/nayuki/QR-Code-generator.git