diff --git a/setup.py b/setup.py
index 04d1691..9227b41 100644
--- a/setup.py
+++ b/setup.py
@@ -27,7 +27,7 @@
 dependencies = [
     "google-api-core[grpc] >= 1.32.0, <3.0.0dev,!=2.0.*,!=2.1.*,!=2.2.*,!=2.3.*,!=2.4.*,!=2.5.*,!=2.6.*,!=2.7.*",
     "proto-plus >= 1.22.0, <2.0.0dev",
-    "protobuf >= 3.20.2, <5.0.0dev",
+    "protobuf>=3.19.5,<5.0.0dev,!=3.20.0,!=3.20.1,!=4.21.0,!=4.21.1,!=4.21.2,!=4.21.3,!=4.21.4,!=4.21.5",
 ]
 
 package_root = os.path.abspath(os.path.dirname(__file__))
diff --git a/testing/constraints-3.7.txt b/testing/constraints-3.7.txt
index df8564d..4005dc5 100644
--- a/testing/constraints-3.7.txt
+++ b/testing/constraints-3.7.txt
@@ -6,4 +6,4 @@
 # Then this file should have google-cloud-foo==1.14.0
 google-api-core==1.32.0
 proto-plus==1.22.0
-protobuf==3.20.2
+protobuf==3.19.5