diff --git a/Dockerfile b/Dockerfile
index 6a97441..0143724 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -16,6 +16,7 @@ RUN apk add --update \
     php-json \
     php-phar \
     php-dom \
+    mbstring \
     && rm -rf /var/cache/apk/*
 
 # Download and make Composer executable