diff --git a/setup.py b/setup.py
index be02dc409..695ffd7d3 100644
--- a/setup.py
+++ b/setup.py
@@ -42,7 +42,7 @@
     "google-cloud-core >= 1.4.1, <3.0.0dev",
     "google-resumable-media >= 0.6.0, < 3.0dev",
     "packaging >= 14.3, <22.0.0dev",
-    "protobuf >= 3.20.2, <5.0.0dev",  # For the legacy proto-based types.
+    "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",  # For the legacy proto-based types.
     "python-dateutil >= 2.7.2, <3.0dev",
     "pyarrow >= 3.0.0, < 10.0dev",
     "requests >= 2.18.0, < 3.0.0dev",
diff --git a/testing/constraints-3.7.txt b/testing/constraints-3.7.txt
index 3b07dc9fa..c9e40d823 100644
--- a/testing/constraints-3.7.txt
+++ b/testing/constraints-3.7.txt
@@ -18,7 +18,7 @@ opentelemetry-instrumentation==0.20b0
 opentelemetry-sdk==1.1.0
 pandas==1.1.0
 proto-plus==1.22.0
-protobuf==3.20.2
+protobuf==3.19.5
 pyarrow==3.0.0
 python-dateutil==2.7.3
 requests==2.18.0