diff --git a/testdata/moonfire-nvr/movement_detection_via_api_ffmpeg.sh b/testdata/moonfire-nvr/movement_detection_via_api_ffmpeg.sh
index 1616374..d0e0f85 100644
--- a/testdata/moonfire-nvr/movement_detection_via_api_ffmpeg.sh
+++ b/testdata/moonfire-nvr/movement_detection_via_api_ffmpeg.sh
@@ -60,7 +60,7 @@ main() {
                threshold="$max_of_last_n"
             fi
          done
-         threshold="$(perl -e "print $threshold + 0.005")"
+         threshold="$(_perl -e "print $threshold + 0.005")"
 
          local has_change=false
          if [ "${#flattened_scores[@]}" -lt 10 ]; then
@@ -99,4 +99,12 @@ _date() {
    fi
 }
 
+_perl() {
+   if which perl &> /dev/null; then
+      perl "$@"
+   else
+      /var/services/homes/squeaky2x3/.nix-profile/bin/perl "$@"
+   fi
+}
+
 main "$@"