diff --git a/frontend/nginx.conf b/frontend/nginx.conf
index 6b7765e9..9a16f008 100644
--- a/frontend/nginx.conf
+++ b/frontend/nginx.conf
@@ -1,3 +1,14 @@
+# Honour the outer reverse proxy's X-Forwarded-Proto when present (e.g. NPM,
+# Traefik, Caddy in front of PicPeak). Falls back to nginx's own $scheme when
+# the header is absent (direct access / no outer proxy). Without this the
+# inner nginx was always forwarding "http" to the backend because the outer
+# proxy → inner nginx hop is plain HTTP, breaking Secure cookies and HTTPS
+# URL generation in the backend. See issue #547.
+map $http_x_forwarded_proto $real_proto {
+    default $http_x_forwarded_proto;
+    ""      $scheme;
+}
+
 server {
     listen 80;
     server_name localhost;
@@ -80,7 +91,7 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_proto;
         proxy_cache_bypass $http_upgrade;
         proxy_read_timeout 86400;
 
@@ -97,7 +108,7 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_proto;
 
         # Cache photos
         proxy_cache_valid 200 302 1d;
@@ -112,7 +123,7 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_proto;
 
         # Cache thumbnails
         proxy_cache_valid 200 302 7d;
@@ -128,7 +139,7 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_proto;
 
         # Cache uploads
         proxy_cache_valid 200 302 7d;
@@ -146,7 +157,7 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_proto;
 
         # Fonts rarely change; cache aggressively (matches backend Cache-Control).
         proxy_cache_valid 200 302 7d;
@@ -161,7 +172,7 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_proto;
     }
 
     # Delegate root requests to backend for public landing page handling
@@ -175,7 +186,7 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_proto;
         proxy_read_timeout 60s;
     }
 
@@ -203,7 +214,7 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_proto;
     }
 
     # SPA fallback
diff --git a/frontend/nginx.dev.conf b/frontend/nginx.dev.conf
index 07692ea1..7506f943 100644
--- a/frontend/nginx.dev.conf
+++ b/frontend/nginx.dev.conf
@@ -1,3 +1,10 @@
+# Honour outer reverse-proxy's X-Forwarded-Proto when present (see #547 /
+# frontend/nginx.conf for full rationale).
+map $http_x_forwarded_proto $real_proto {
+    default $http_x_forwarded_proto;
+    ""      $scheme;
+}
+
 server {
     listen 80;
     server_name localhost;
@@ -10,7 +17,7 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_proto;
     }
 
     # Photos proxy to backend
@@ -41,7 +48,7 @@ server {
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_set_header X-Forwarded-Proto $real_proto;
     }
 
     # SPA fallback