diff --git a/Dockerfile.r4se.2-rootfs b/Dockerfile.r4se.2-rootfs
index 43b350c..42657ef 100644
--- a/Dockerfile.r4se.2-rootfs
+++ b/Dockerfile.r4se.2-rootfs
@@ -3,7 +3,7 @@ LABEL maintainer=admin@licsber.site
 
 RUN cd friendlywrt && \
     export SOC_CFLAGS="-march=armv8-a+crypto+crc -mcpu=cortex-a73.cortex-a53+crypto+crc -mtune=cortex-a73.cortex-a53" && \
-    make -j$($(nproc)+1) || make -j1 V=s && \
+    make -j$(($(nproc)+1)) || make -j1 V=s && \
     echo $?
 
 RUN source .current_config.mk && \