diff --git a/requirements.txt b/requirements.txt
index 6c8ce408f..8f5b324ba 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,3 +7,4 @@ tornado>=5.0.0
 esptool>=2.3.1
 typing>=3.0.0
 protobuf>=3.4
+pyserial>=3.4,<4
diff --git a/setup.py b/setup.py
index cb470e04e..87fd6b778 100755
--- a/setup.py
+++ b/setup.py
@@ -32,6 +32,7 @@ REQUIRES = [
     'typing>=3.0.0;python_version<"3.5"',
     'protobuf>=3.4',
     'tzlocal>=1.4',
+    'pyserial>=3.4,<4',
 ]
 
 CLASSIFIERS = [