diff --git a/setup.py b/setup.py
index 73911a2910..71f9ec61b5 100644
--- a/setup.py
+++ b/setup.py
@@ -28,7 +28,7 @@
     "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.*",
     "google-cloud-core >= 1.4.1, <3.0.0dev",
     "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",
 ]
 extras = {}
 
diff --git a/testing/constraints-3.7.txt b/testing/constraints-3.7.txt
index c96e62aae1..21daf4a512 100644
--- a/testing/constraints-3.7.txt
+++ b/testing/constraints-3.7.txt
@@ -8,4 +8,4 @@
 google-api-core==1.32.0
 google-cloud-core==1.4.1
 proto-plus==1.22.0
-protobuf==3.20.2  # transitive from `google-api-core`
+protobuf==3.19.5  # transitive from `google-api-core`