diff --git a/setup.py b/setup.py
index 38f6d0e6ee..b779b4ce18 100644
--- a/setup.py
+++ b/setup.py
@@ -37,7 +37,7 @@
     "google-cloud-core >= 1.4.1, <3.0.0dev",
     "proto-plus >= 1.22.0, <2.0.0dev",
     "proto-plus >= 1.22.2, <2.0.0dev; python_version>='3.11'",
-    "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",
+    "protobuf>=3.20.2,<6.0.0dev,!=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 1470ab1b89..2e9ab779bf 100644
--- a/testing/constraints-3.7.txt
+++ b/testing/constraints-3.7.txt
@@ -9,4 +9,4 @@ google-api-core==1.34.0
 google-auth==2.14.1
 google-cloud-core==1.4.1
 proto-plus==1.22.0
-protobuf==3.19.5  # transitive from `google-api-core`
+protobuf==3.20.2  # transitive from `google-api-core`