diff --git a/frp/v0.21.0/Dockerfile b/frp/v0.21.0/Dockerfile
index 83eff5c..16bda3b 100644
--- a/frp/v0.21.0/Dockerfile
+++ b/frp/v0.21.0/Dockerfile
@@ -8,12 +8,12 @@ USER root
 RUN apk add --no-cache openssl
 
 # Install frp
-ENV FRP_VER 0.21.0
+ENV VERSION 0.21.0
 
-RUN wget -O frp.tar.gz https://github.com/fatedier/frp/releases/download/v$FRP_VER/frp_$FRP_VER_linux_amd64.tar.gz && \
+RUN wget -O frp.tar.gz https://github.com/fatedier/frp/releases/download/v${VERSION}/frp_${VERSION}_linux_amd64.tar.gz && \
 	tar -xzf frp.tar.gz -C / && rm frp.tar.gz
 
-RUN ln -s /frp_$FRP_VER_linux_amd64 /frp
+RUN ln -s /frp_$VERSION_linux_amd64 /frp
 
 WORKDIR /frp