diff --git a/google-cloud-speech/setup.py b/google-cloud-speech/setup.py
index 416c22732d00..5e1ad39e0f49 100644
--- a/google-cloud-speech/setup.py
+++ b/google-cloud-speech/setup.py
@@ -33,7 +33,8 @@
     # Until this issue is closed
     # https://github.com/googleapis/google-cloud-python/issues/10566
     "google-api-core[grpc] >= 1.31.5, <3.0.0dev,!=2.0.*,!=2.1.*,!=2.2.*,!=2.3.0",
-    "proto-plus >= 1.15.0",
+    "proto-plus >= 1.15.0, <2.0.0dev",
+    "protobuf >= 3.19.0, <4.0.0dev",
 ]
 extras = {"libcst": "libcst >= 0.2.5"}
 
diff --git a/google-cloud-speech/testing/constraints-3.6.txt b/google-cloud-speech/testing/constraints-3.6.txt
index 2bdebaf039b3..3ef972c666c5 100644
--- a/google-cloud-speech/testing/constraints-3.6.txt
+++ b/google-cloud-speech/testing/constraints-3.6.txt
@@ -8,3 +8,4 @@
 google-api-core==1.31.5
 libcst==0.2.5
 proto-plus==1.15.0
+protobuf==3.19.0