diff --git a/buildscripts/kokoro/macos.cfg b/buildscripts/kokoro/macos.cfg
index b7d1dd7d4d..50c0da6cdc 100644
--- a/buildscripts/kokoro/macos.cfg
+++ b/buildscripts/kokoro/macos.cfg
@@ -4,6 +4,14 @@
 build_file: "grpc-java/buildscripts/kokoro/unix.sh"
 timeout_mins: 45
 
+# We had problems with random tests timing out because it took seconds to do
+# trivial (ns) operations. The Mac machines have 2 cores with 4 logical
+# threads, so Gradle should be using 4 workers by default.
+env_vars {
+  key: "GRADLE_FLAGS"
+  value: "--max-workers=2"
+}
+
 # We always build mvn artifacts.
 action {
   define_artifacts {
diff --git a/buildscripts/kokoro/unix.sh b/buildscripts/kokoro/unix.sh
index 27a50143aa..3106f00793 100755
--- a/buildscripts/kokoro/unix.sh
+++ b/buildscripts/kokoro/unix.sh
@@ -30,7 +30,7 @@ ARCH="$ARCH" buildscripts/make_dependencies.sh
 
 # Set properties via flags, do not pollute gradle.properties
 GRADLE_FLAGS="${GRADLE_FLAGS:-}"
-GRADLE_FLAGS+=" -PtargetArch=x86_$ARCH $GRADLE_FLAGS"
+GRADLE_FLAGS+=" -PtargetArch=x86_$ARCH"
 GRADLE_FLAGS+=" -Pcheckstyle.ignoreFailures=false"
 GRADLE_FLAGS+=" -PfailOnWarnings=true"
 GRADLE_FLAGS+=" -PerrorProne=true"