diff --git a/Dockerfile b/Dockerfile
index 4101443..c8788f2 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -29,6 +29,7 @@ RUN apk add --no-cache wget \
 
 # Install php extensions
 RUN docker-php-ext-install -j$(nproc) \
+	calendar \
 	bcmath \
 	bz2 \
 	curl \