diff --git a/cirq-core/requirements.txt b/cirq-core/requirements.txt
index ef23cdf53de..b526c835455 100644
--- a/cirq-core/requirements.txt
+++ b/cirq-core/requirements.txt
@@ -1,6 +1,6 @@
 # Runtime requirements for the python 3 version of cirq.
 
-attrs
+attrs>=21.3.0
 duet>=0.2.8
 matplotlib~=3.0
 networkx>=2.4