diff --git a/docker/frontend-entrypoint.sh b/docker/frontend-entrypoint.sh
index ff529749..f42b0f7b 100644
--- a/docker/frontend-entrypoint.sh
+++ b/docker/frontend-entrypoint.sh
@@ -2,7 +2,6 @@
 set -eu
 
 THT_FRONTEND_API_UPSTREAM=${THT_FRONTEND_API_UPSTREAM:-http://core:8787}
-THT_FRONTEND_API_UPSTREAM=${THT_FRONTEND_API_UPSTREAM%/}
 if ! /usr/local/bin/validate-frontend-api-upstream "$THT_FRONTEND_API_UPSTREAM"; then
   echo "Invalid THT_FRONTEND_API_UPSTREAM: expected internal http://core:8787" >&2
   exit 2
diff --git a/docker/smoke/frontend-policy-smoke.sh b/docker/smoke/frontend-policy-smoke.sh
index d4d7c6b6..ff8f6bae 100755
--- a/docker/smoke/frontend-policy-smoke.sh
+++ b/docker/smoke/frontend-policy-smoke.sh
@@ -32,16 +32,24 @@ if rg -n 'BACKEND_BASE_URL|VITE_BACKEND_URL' docker/frontend-entrypoint.sh docke
 fi
 
 upstream_validator=docker/validate-frontend-api-upstream.sh
-for upstream in http://core:8787 http://core:8787/; do
+for upstream in http://core:8787; do
   if ! "$upstream_validator" "$upstream"; then
     echo "frontend upstream validator rejected $upstream" >&2
     exit 1
   fi
 done
 
+if grep -Fq 'THT_FRONTEND_API_UPSTREAM=${THT_FRONTEND_API_UPSTREAM%/}' docker/frontend-entrypoint.sh; then
+  echo "frontend entrypoint must not normalize an upstream path component" >&2
+  exit 1
+fi
+
 for upstream in \
   https://core:8787 \
   http://core:8080 \
+  http://core:8787/ \
+  http://core:8787// \
+  http://core:8787/// \
   http://core:8787/api \
   http://user:pass@core:8787 \
   'http://core:8787?next=evil' \
diff --git a/docker/validate-frontend-api-upstream.sh b/docker/validate-frontend-api-upstream.sh
index 65e4de27..4e2243c5 100755
--- a/docker/validate-frontend-api-upstream.sh
+++ b/docker/validate-frontend-api-upstream.sh
@@ -1,7 +1,4 @@
 #!/bin/sh
 set -eu
 
-case "${1-}" in
-  http://core:8787|http://core:8787/) exit 0 ;;
-  *) exit 2 ;;
-esac
+[ "${1-}" = "http://core:8787" ]