diff --git a/internal/kokoro/check_incompat_changes.sh b/internal/kokoro/check_incompat_changes.sh
new file mode 100755
index 0000000..a93d8a8
--- /dev/null
+++ b/internal/kokoro/check_incompat_changes.sh
@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+
+# Display commands being run
+set -x
+
+# Only run apidiff checks on go1.11 (we only need it once).
+# TODO(deklerk) We should pass an environment variable from kokoro to decide
+# this logic instead.
+if [[ `go version` != *"go1.11"* ]]; then
+    exit 0
+fi
+
+try3() { eval "$*" || eval "$*" || eval "$*"; }
+
+try3 go get -u golang.org/x/exp/cmd/apidiff
+
+# We compare against master@HEAD. This is unfortunate in some cases: if you're
+# working on an out-of-date branch, and master gets some new feature (that has
+# nothing to do with your work on your branch), you'll get an error message.
+# Thankfully the fix is quite simple: rebase your branch.
+git clone https://github.com/googleapis/gax-go /tmp/gax
+
+for dir in "" "/v2"; do
+  pkg="github.com/googleapis/gax-go$dir"
+  echo "Testing $pkg"
+
+  # cd to the exact directory that specifies the go module so that it doesn't
+  # use the module cache. https://go-review.googlesource.com/c/exp/+/155058
+  cd "/tmp/gax$dir"
+  apidiff -w /tmp/pkg.master $pkg
+  cd - > /dev/null
+
+  # TODO(deklerk) there's probably a nicer way to do this that doesn't require
+  # two invocations
+  if ! apidiff /tmp/pkg.master $pkg | (! read); then
+    apidiff /tmp/pkg.master $pkg
+    exit 1
+  fi
+done
diff --git a/internal/kokoro/test.sh b/internal/kokoro/test.sh
index 6446d94..40f6edd 100755
--- a/internal/kokoro/test.sh
+++ b/internal/kokoro/test.sh
@@ -27,6 +27,7 @@
 try3 go get -v -t ./...
 
 ./internal/kokoro/vet.sh
+./internal/kokoro/check_incompat_changes.sh
 
 # Run tests and tee output to log file, to be pushed to GCS as artifact.
-go test -race -v ./... 2>&1 | tee $KOKORO_ARTIFACTS_DIR/$KOKORO_GERRIT_CHANGE_NUMBER.txt
\ No newline at end of file
+go test -race -v ./... 2>&1 | tee $KOKORO_ARTIFACTS_DIR/$KOKORO_GERRIT_CHANGE_NUMBER.txt