diff --git a/docker/Dockerfile b/docker/Dockerfile
index c6da2efd..e47dc5d7 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -55,7 +55,7 @@ COPY . .
 RUN git checkout "$SHAIRPORT_SYNC_BRANCH"
 WORKDIR /shairport-sync/build
 RUN autoreconf -i ../
-RUN ../configure --sysconfdir=/etc --with-alsa --with-pa --with-soxr --with-avahi --with-ssl=openssl \
+RUN CFLAGS="-O3" CXXFLAGS="-O3" ../configure --sysconfdir=/etc --with-alsa --with-pa --with-soxr --with-avahi --with-ssl=openssl \
         --with-airplay-2 --with-metadata --with-dummy --with-pipe --with-dbus-interface \
         --with-stdout --with-mpris-interface --with-mqtt-client \
         --with-apple-alac --with-convolution
diff --git a/docker/classic/Dockerfile b/docker/classic/Dockerfile
index d5978410..d41cac4f 100644
--- a/docker/classic/Dockerfile
+++ b/docker/classic/Dockerfile
@@ -40,7 +40,7 @@ COPY . .
 RUN git checkout "$SHAIRPORT_SYNC_BRANCH"
 WORKDIR /shairport-sync/build
 RUN autoreconf -i ../
-RUN ../configure --sysconfdir=/etc --with-alsa --with-pa --with-soxr --with-avahi --with-ssl=mbedtls \
+RUN CFLAGS="-O3" CXXFLAGS="-O3" ../configure --sysconfdir=/etc --with-alsa --with-pa --with-soxr --with-avahi --with-ssl=mbedtls \
         --with-metadata --with-dummy --with-pipe --with-dbus-interface \
         --with-stdout --with-mpris-interface --with-mqtt-client \
         --with-apple-alac --with-convolution
diff --git a/docker/classic/etc/s6-overlay/s6-rc.d/01-startup/script.sh b/docker/classic/etc/s6-overlay/s6-rc.d/01-startup/script.sh
index 3037e98a..253c0afa 100644
--- a/docker/classic/etc/s6-overlay/s6-rc.d/01-startup/script.sh
+++ b/docker/classic/etc/s6-overlay/s6-rc.d/01-startup/script.sh
@@ -1,2 +1,5 @@
 #!/bin/sh
 echo "STARTING - $(date)"
+
+# Set the limit to the same value Docker has been using in earlier version.
+ulimit -n 1048576
diff --git a/docker/etc/s6-overlay/s6-rc.d/01-startup/script.sh b/docker/etc/s6-overlay/s6-rc.d/01-startup/script.sh
index 3037e98a..253c0afa 100644
--- a/docker/etc/s6-overlay/s6-rc.d/01-startup/script.sh
+++ b/docker/etc/s6-overlay/s6-rc.d/01-startup/script.sh
@@ -1,2 +1,5 @@
 #!/bin/sh
 echo "STARTING - $(date)"
+
+# Set the limit to the same value Docker has been using in earlier version.
+ulimit -n 1048576