diff --git a/packages/google-cloud-service-directory/setup.py b/packages/google-cloud-service-directory/setup.py
index 787a0857a3c5..4243d7ad27ba 100644
--- a/packages/google-cloud-service-directory/setup.py
+++ b/packages/google-cloud-service-directory/setup.py
@@ -43,7 +43,7 @@
     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",
         "grpc-google-iam-v1 >= 0.12.4, <1.0.0dev",
     ),
     python_requires=">=3.7",
diff --git a/packages/google-cloud-service-directory/testing/constraints-3.7.txt b/packages/google-cloud-service-directory/testing/constraints-3.7.txt
index c52b1ed7baa8..fb33557f4bd0 100644
--- a/packages/google-cloud-service-directory/testing/constraints-3.7.txt
+++ b/packages/google-cloud-service-directory/testing/constraints-3.7.txt
@@ -8,4 +8,4 @@
 google-api-core==1.32.0
 proto-plus==1.22.0
 grpc-google-iam-v1==0.12.4
-protobuf==3.20.2
+protobuf==3.19.5