diff --git a/setup.py b/setup.py
index 482e43d831..d589d6dd0d 100644
--- a/setup.py
+++ b/setup.py
@@ -130,7 +130,7 @@
     install_requires=(
         "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",
         "packaging >= 14.3, <22.0.0dev",
         "google-cloud-storage >= 1.32.0, < 3.0.0dev",
         "google-cloud-bigquery >= 1.15.0, < 3.0.0dev",
diff --git a/testing/constraints-3.7.txt b/testing/constraints-3.7.txt
index 9e4b10a280..7d52895102 100644
--- a/testing/constraints-3.7.txt
+++ b/testing/constraints-3.7.txt
@@ -8,7 +8,7 @@
 google-api-core==1.32.0
 libcst==0.2.5
 proto-plus==1.22.0
-protobuf==3.20.2
+protobuf==3.19.5
 mock==4.0.2
 google-cloud-storage==1.32.0
 google-auth==1.25.0  # TODO: Remove when google-api-core >= 1.26.0 is required