diff --git a/.gitmodules b/.gitmodules
index b1b93f161..2477762b8 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -32,3 +32,6 @@
 [submodule "external/cpr"]
 	path = external/cpr
 	url = https://github.com/whoshuu/cpr
+[submodule "external/ngtcp2"]
+	path = external/ngtcp2
+	url = https://github.com/ngtcp2/ngtcp2.git
diff --git a/external/ngtcp2 b/external/ngtcp2
new file mode 160000
index 000000000..51e95c8d8
--- /dev/null
+++ b/external/ngtcp2
@@ -0,0 +1 @@
+Subproject commit 51e95c8d8972abd69515d9790e8fbb774262d9ea