diff --git a/5.018.004-64bit,threaded/Dockerfile b/5.018.004-64bit,threaded/Dockerfile
index 1d026e8..bab717b 100644
--- a/5.018.004-64bit,threaded/Dockerfile
+++ b/5.018.004-64bit,threaded/Dockerfile
@@ -14,7 +14,7 @@ RUN curl -SL https://cpan.metacpan.org/authors/id/R/RJ/RJBS/perl-5.18.4.tar.bz2
     && rm perl-5.18.4.tar.bz2 \
     && ./Configure -Dusethreads -Duse64bitall -A ccflags=-fwrapv -des \
     && make -j$(nproc) \
-    && TEST_JOBS=$(nproc) make test_harness \
+    && make test_harness \
     && make install \
     && cd /usr/src \
     && curl -LO https://raw.githubusercontent.com/miyagawa/cpanminus/master/cpanm \
diff --git a/5.018.004-64bit/Dockerfile b/5.018.004-64bit/Dockerfile
index b64bac0..46af98a 100644
--- a/5.018.004-64bit/Dockerfile
+++ b/5.018.004-64bit/Dockerfile
@@ -14,7 +14,7 @@ RUN curl -SL https://cpan.metacpan.org/authors/id/R/RJ/RJBS/perl-5.18.4.tar.bz2
     && rm perl-5.18.4.tar.bz2 \
     && ./Configure -Duse64bitall -A ccflags=-fwrapv -des \
     && make -j$(nproc) \
-    && TEST_JOBS=$(nproc) make test_harness \
+    && make test_harness \
     && make install \
     && cd /usr/src \
     && curl -LO https://raw.githubusercontent.com/miyagawa/cpanminus/master/cpanm \
diff --git a/5.020.002-64bit,threaded/Dockerfile b/5.020.002-64bit,threaded/Dockerfile
index 7eb9236..0db14bd 100644
--- a/5.020.002-64bit,threaded/Dockerfile
+++ b/5.020.002-64bit,threaded/Dockerfile
@@ -14,7 +14,7 @@ RUN curl -SL https://cpan.metacpan.org/authors/id/S/SH/SHAY/perl-5.20.2.tar.bz2
     && rm perl-5.20.2.tar.bz2 \
     && ./Configure -Dusethreads -Duse64bitall  -des \
     && make -j$(nproc) \
-    && TEST_JOBS=$(nproc) make test_harness \
+    && make test_harness \
     && make install \
     && cd /usr/src \
     && curl -LO https://raw.githubusercontent.com/miyagawa/cpanminus/master/cpanm \
diff --git a/5.020.002-64bit/Dockerfile b/5.020.002-64bit/Dockerfile
index 5d2ef2b..1d153b4 100644
--- a/5.020.002-64bit/Dockerfile
+++ b/5.020.002-64bit/Dockerfile
@@ -14,7 +14,7 @@ RUN curl -SL https://cpan.metacpan.org/authors/id/S/SH/SHAY/perl-5.20.2.tar.bz2
     && rm perl-5.20.2.tar.bz2 \
     && ./Configure -Duse64bitall  -des \
     && make -j$(nproc) \
-    && TEST_JOBS=$(nproc) make test_harness \
+    && make test_harness \
     && make install \
     && cd /usr/src \
     && curl -LO https://raw.githubusercontent.com/miyagawa/cpanminus/master/cpanm \
diff --git a/Releases.yaml b/Releases.yaml
index 3deaea5..c754781 100644
--- a/Releases.yaml
+++ b/Releases.yaml
@@ -15,7 +15,9 @@ releases:
     sha1:    69c34558a0a939a7adbbc1de48c06ea418d81e27
     pause:   RJBS
     extra_flags: "-A ccflags=-fwrapv"
+    test_parallel: no
 
   - version: 5.20.2
     sha1:    63126c683b4c79c35008a47d56f7beae876c569f
     pause:   SHAY
+    test_parallel: no