diff --git a/Dockerfile b/Dockerfile
index 45d9743..690594f 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,7 +1,7 @@
 FROM openjdk:8-jre-alpine
 ENV AOZORA_EPUB3 AozoraEpub3-1.1.0b46.zip
 ENV KINDLEGEN kindlegen_linux_2.6_i386_v2_9.tar.gz
-ENV NAROU_VERSION 3.1.1
+ENV NAROU_VERSION 3.1.2
 WORKDIR /opt/narou
 
 RUN apk --update add ruby ruby-io-console ruby-json wget unzip && rm -rf /var/cache/apk/*
@@ -14,7 +14,6 @@ RUN wget http://kindlegen.s3.amazonaws.com/${KINDLEGEN} && \
     tar zxf ${KINDLEGEN} -C /opt/kindlegen && \
     rm ${KINDLEGEN}
 
-COPY narou-3.1.1.gem .
 RUN gem install narou -v ${NAROU_VERSION} --no-document
 
 COPY init.sh /usr/local/bin
diff --git a/narou-3.1.1.gem b/narou-3.1.1.gem
deleted file mode 100644
index 036fc01..0000000
Binary files a/narou-3.1.1.gem and /dev/null differ