diff --git a/requirements.txt b/requirements.txt
index dad5ce413b..4b64dadd0b 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -29,7 +29,8 @@ kconfiglib==13.7.1
 
 # esptool requirements (see components/esptool_py/esptool/setup.py)
 reedsolo>=1.5.3,<=1.5.4
-bitstring>=3.1.6
+# bitstring 4 dropped support for Python 3.6 and older
+bitstring>=3.1.6,<4
 ecdsa>=0.16.0
 
 # espcoredump requirements