diff --git a/setup.py b/setup.py
index 5a8767c..30e1fc6 100644
--- a/setup.py
+++ b/setup.py
@@ -46,7 +46,7 @@
     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",
     ),
     python_requires=">=3.7",
     classifiers=[
diff --git a/testing/constraints-3.7.txt b/testing/constraints-3.7.txt
index bc6059c..a12652c 100644
--- a/testing/constraints-3.7.txt
+++ b/testing/constraints-3.7.txt
@@ -21,4 +21,4 @@
 # Then this file should have foo==1.14.0
 google-api-core==1.32.0
 proto-plus==1.22.0
-protobuf==3.20.2
+protobuf==3.19.5