diff --git a/Dockerfile b/Dockerfile
index 84f2dcce5..a13c6e549 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -5,28 +5,30 @@ COPY composer.json /
 FROM scratch AS test_source
 
 COPY benchmarks/ benchmarks/
-COPY lib/ /lib/
 COPY src/ /src/
 COPY tests/ /tests/
 COPY phpunit.xml.* phpstan.neon.* .php_cs.* phpbench.json /
 
 FROM alpine:3.9
 
+ADD https://dl.bintray.com/php-alpine/key/php-alpine.rsa.pub /etc/apk/keys/php-alpine.rsa.pub
+
+RUN apk --update add ca-certificates && \
+    echo "https://dl.bintray.com/php-alpine/v3.9/php-7.4" >> /etc/apk/repositories
+
 # alpine php package does not include default extensions, be explicit
 RUN set -eu; \
     apk add --no-cache \
-        php7 \
-        php7-iconv \
-        php7-json \
-        php7-mbstring \
-        php7-openssl \
-        php7-phar \
-        php7-tokenizer \
-        php7-xml \
-        php7-xmlwriter \
-        php7-dom \
-        php7-pdo \
-    ;
+        php \
+        php-iconv \
+        php-json \
+        php-mbstring \
+        php-openssl \
+        php-phar \
+        php-xml \
+        php-dom \
+        php-pdo \
+    ; ln -s /usr/bin/php7 /usr/bin/php
 
 COPY --from=composer:latest /usr/bin/composer /usr/bin/composer
 
@@ -34,7 +36,7 @@ WORKDIR /opt/test
 
 COPY --from=composer_install_requirements / .
 
-RUN composer install
+RUN php7 /usr/bin/composer install
 
 COPY --from=test_source / .