diff --git a/README.md b/README.md
index 47333a37..c75b86e3 100644
--- a/README.md
+++ b/README.md
@@ -272,6 +272,11 @@ services:
       syncious_production_instance: "https://syncious.example.com"
 ```
 
+Add these additional environment variables to Materialious.
+```yaml
+VITE_DEFAULT_SYNCIOUS_INSTANCE: "https://syncious.example.com"
+```
+
 ## Step 6 (Optional): Self-host PeerJS
 [Read the official guide.](https://github.com/peers/peerjs-server?tab=readme-ov-file#docker)
 
diff --git a/materialious/Dockerfile b/materialious/Dockerfile
index b9c123fc..c5f3d3e3 100644
--- a/materialious/Dockerfile
+++ b/materialious/Dockerfile
@@ -18,6 +18,7 @@ RUN echo "VITE_DEFAULT_INVIDIOUS_INSTANCE=VITE_DEFAULT_INVIDIOUS_INSTANCE_PLACEH
     echo "VITE_DEFAULT_PEERJS_HOST=VITE_DEFAULT_PEERJS_HOST_PLACEHOLDER" >> .env && \
     echo "VITE_DEFAULT_PEERJS_PATH=VITE_DEFAULT_PEERJS_PATH_PLACEHOLDER" >> .env && \
     echo "VITE_DEFAULT_PEERJS_PORT=VITE_DEFAULT_PEERJS_PORT_PLACEHOLDER" >> .env && \
+    echo "VITE_DEFAULT_SYNCIOUS_INSTANCE=VITE_DEFAULT_SYNCIOUS_INSTANCE_PLACEHOLDER" >> .env && \
     echo "VITE_DEFAULT_RETURNYTDISLIKES_INSTANCE=VITE_DEFAULT_RETURNYTDISLIKES_INSTANCE_PLACEHOLDER" >> .env
 
 # Install dependencies and build the project
diff --git a/materialious/replace_env_vars.sh b/materialious/replace_env_vars.sh
index 5d5e419d..f624262f 100644
--- a/materialious/replace_env_vars.sh
+++ b/materialious/replace_env_vars.sh
@@ -11,3 +11,4 @@ find "$ROOT_DIR" -type f \( -name "*.js" -o -name "*.html" \) -exec sed -i 's|VI
 find "$ROOT_DIR" -type f \( -name "*.js" -o -name "*.html" \) -exec sed -i 's|VITE_DEFAULT_PEERJS_HOST_PLACEHOLDER|'"$VITE_DEFAULT_PEERJS_HOST"'|g' {} +
 find "$ROOT_DIR" -type f \( -name "*.js" -o -name "*.html" \) -exec sed -i 's|VITE_DEFAULT_PEERJS_PATH_PLACEHOLDER|'"$VITE_DEFAULT_PEERJS_PATH"'|g' {} +
 find "$ROOT_DIR" -type f \( -name "*.js" -o -name "*.html" \) -exec sed -i 's|VITE_DEFAULT_PEERJS_PORT_PLACEHOLDER|'"$VITE_DEFAULT_PEERJS_PORT"'|g' {} +
+find "$ROOT_DIR" -type f \( -name "*.js" -o -name "*.html" \) -exec sed -i 's|VITE_DEFAULT_SYNCIOUS_INSTANCE_PLACEHOLDER|'"$VITE_DEFAULT_SYNCIOUS_INSTANCE"'|g' {} +