diff --git a/Dockerfile b/Dockerfile
index 4bfc8b71c30e12fb865279b02759b101d370c8af..5e80385597eed6b9cec38914cb8c84e67df9ddb4 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -35,7 +35,7 @@ ENV NODE_ENV "production"
 
 RUN [ "npx", "pubsweet", "build"]
 
-EXPOSE ${PORT:3000}
+EXPOSE ${PORT:-3000}
 
 CMD []
 
diff --git a/Dockerfile-development b/Dockerfile-development
index 8b2c83b515839aca27d27ba991d9f911f4571959..93c2ee289189e582eeada37eff720419a02853a5 100644
--- a/Dockerfile-development
+++ b/Dockerfile-development
@@ -9,6 +9,6 @@ COPY webpack webpack
 COPY config config
 COPY app app
 
-EXPOSE ${PORT:3000}
+EXPOSE ${PORT:-3000}
 
 CMD []