diff --git a/php-apache/Dockerfile b/php-apache/Dockerfile
index 621c8b0..778ce09 100644
--- a/php-apache/Dockerfile
+++ b/php-apache/Dockerfile
@@ -66,7 +66,8 @@ RUN set -ex; \
 	curl -o roundcubemail.tar.gz -SL https://github.com/roundcube/roundcubemail/releases/download/${ROUNDCUBEMAIL_VERSION}/roundcubemail-${ROUNDCUBEMAIL_VERSION}-complete.tar.gz; \
 	curl -o roundcubemail.tar.gz.asc -SL https://github.com/roundcube/roundcubemail/releases/download/${ROUNDCUBEMAIL_VERSION}/roundcubemail-${ROUNDCUBEMAIL_VERSION}-complete.tar.gz.asc; \
 	export GNUPGHOME="$(mktemp -d)"; \
-	gpg --keyserver ha.pool.sks-keyservers.net --recv-keys F3E4C04BB3DB5D4215C45F7F5AB2BAA141C4F7D5; \
+	# ha.pool.sks-keyservers.net seems to be unreliable, use pgp.mit.edu as fallback
+	gpg --keyserver ha.pool.sks-keyservers.net --recv-keys F3E4C04BB3DB5D4215C45F7F5AB2BAA141C4F7D5 || gpg --keyserver pgp.mit.edu --recv-keys F3E4C04BB3DB5D4215C45F7F5AB2BAA141C4F7D5; \
 	gpg --batch --verify roundcubemail.tar.gz.asc roundcubemail.tar.gz; \
 	tar -xzf roundcubemail.tar.gz -C /usr/src/; \
 	gpgconf --kill all; \
diff --git a/php-fpm/Dockerfile b/php-fpm/Dockerfile
index 85a77d2..f0db357 100644
--- a/php-fpm/Dockerfile
+++ b/php-fpm/Dockerfile
@@ -63,7 +63,8 @@ RUN set -ex; \
 	curl -o roundcubemail.tar.gz -SL https://github.com/roundcube/roundcubemail/releases/download/${ROUNDCUBEMAIL_VERSION}/roundcubemail-${ROUNDCUBEMAIL_VERSION}-complete.tar.gz; \
 	curl -o roundcubemail.tar.gz.asc -SL https://github.com/roundcube/roundcubemail/releases/download/${ROUNDCUBEMAIL_VERSION}/roundcubemail-${ROUNDCUBEMAIL_VERSION}-complete.tar.gz.asc; \
 	export GNUPGHOME="$(mktemp -d)"; \
-	gpg --keyserver ha.pool.sks-keyservers.net --recv-keys F3E4C04BB3DB5D4215C45F7F5AB2BAA141C4F7D5; \
+	# ha.pool.sks-keyservers.net seems to be unreliable, use pgp.mit.edu as fallback
+	gpg --keyserver ha.pool.sks-keyservers.net --recv-keys F3E4C04BB3DB5D4215C45F7F5AB2BAA141C4F7D5 || gpg --keyserver pgp.mit.edu --recv-keys F3E4C04BB3DB5D4215C45F7F5AB2BAA141C4F7D5; \
 	gpg --batch --verify roundcubemail.tar.gz.asc roundcubemail.tar.gz; \
 	tar -xzf roundcubemail.tar.gz -C /usr/src/; \
 	gpgconf --kill all; \