diff --git a/zsh/.bash_profile.google b/zsh/.bash_profile.google
index e8e1390..004e725 100644
--- a/zsh/.bash_profile.google
+++ b/zsh/.bash_profile.google
@@ -74,6 +74,17 @@ export PATH=$PATH:/usr/local/google/home/cnieves/.local/binexport PATH=$PATH:/us
 
 source ~/fzf-at-google.zsh
 
+# Temporary definition for knock, which will override itself with the
+# real implementation.
+knock() {
+  if gcertstatus --nocheck_ssh &>/dev/null; then
+    source /google/bin/releases/knock/knock.sh
+    knock "$@"  # Call the real implementation and pass any parameters.
+  else
+    echo "ERROR: Cannot invoke knock before gcert has been run" >&2
+  fi
+}
+
 sl() {
   blaze build --config gmscore_arm64 //java/com/google/android/gmscore/$1:$2