diff --git a/docker-setup.sh b/docker-setup.sh
index 0395d20f4..ffbfc1493 100755
--- a/docker-setup.sh
+++ b/docker-setup.sh
@@ -129,7 +129,7 @@ upsert_env() {
   local -a keys=("$@")
   local tmp
   tmp="$(mktemp)"
-  declare -A seen=()
+  local seen_keys=""
 
   if [[ -f "$file" ]]; then
     while IFS= read -r line || [[ -n "$line" ]]; do
@@ -138,7 +138,7 @@ upsert_env() {
       for k in "${keys[@]}"; do
         if [[ "$key" == "$k" ]]; then
           printf '%s=%s\n' "$k" "${!k-}" >>"$tmp"
-          seen["$k"]=1
+          seen_keys+="|$k|"
           replaced=true
           break
         fi
@@ -150,7 +150,7 @@ upsert_env() {
   fi
 
   for k in "${keys[@]}"; do
-    if [[ -z "${seen[$k]:-}" ]]; then
+    if [[ "$seen_keys" != *"|$k|"* ]]; then
       printf '%s=%s\n' "$k" "${!k-}" >>"$tmp"
     fi
   done