diff --git a/.gitignore b/.gitignore
index 7162e10..a47adf1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@ __pycache__/
 *.pyo
 *.pyc
 *.json
+*.gz
diff --git a/run.sh b/run.sh
index 57f093d..a3e889e 100755
--- a/run.sh
+++ b/run.sh
@@ -13,8 +13,10 @@ previous_file=""
 while true; do
 	# Get one shot of data
 	data="$("$PYTHON" "$(dirname "$0")"/trainmap_backup.py)"
+	if test $? -ne 0; then echo "Error: failed to fetch trainmap data" >&2; continue; fi
 
 	timestamp="$(printf '%s\n' "$data" | jq ".timestamp / 1000 | round")"
+	if test "$timestamp" = "" || test "$timestamp" -lt 1705410073 || test "$timestamp" -gt 4102441200; then echo "Error: timestamp '$timestamp' invalid" >&2; continue; fi
 	file="$(date +%Y-%m-%d --date "@$timestamp").json"
 
 	# Write the data to file
@@ -23,8 +25,12 @@ while true; do
 	# At the start of a new day, archive the previous day's file
 	if test "$previous_file" == ""; then
 		previous_file="$file"
-	elif test "$file" != "$previous_file" && test "$file" != ""; then
-		gzip --best "$previous_file"
+	elif test "$file" != "$previous_file"; then
+		if test -e "$previous_file.gz"; then
+			echo "Warning: $previous_file.gz already exists, not archiving" >&2
+		else
+			gzip --best "$previous_file"
+		fi
 		previous_file="$file"
 	fi