diff --git a/playbooks/run-libraries-unit-tests.yaml b/playbooks/run-libraries-unit-tests.yaml
index 7012c1b38..fbb26fd10 100644
--- a/playbooks/run-libraries-unit-tests.yaml
+++ b/playbooks/run-libraries-unit-tests.yaml
@@ -5,7 +5,12 @@
           set -e
           set -x
           if [ "{{ puppet_gem_version }}" != "latest" ]; then
-            export PUPPET_GEM_VERSION='~> {{ puppet_gem_version }}.0'
+            if [ "{{ puppet_gem_version }}" == "5.5" ]; then
+              # Pin to 5.5.6. See PUP-9270 and PUP-9271
+              export PUPPET_GEM_VERSION='{{ puppet_gem_version }}.6'
+            else
+              export PUPPET_GEM_VERSION='~> {{ puppet_gem_version }}.0'
+            fi
           fi
           ./run_unit_tests.sh
         executable: /bin/bash
diff --git a/playbooks/run-unit-tests.yaml b/playbooks/run-unit-tests.yaml
index 81b9ddab3..9f151473f 100644
--- a/playbooks/run-unit-tests.yaml
+++ b/playbooks/run-unit-tests.yaml
@@ -3,7 +3,12 @@
     - shell:
         cmd: |
           if [ "{{ puppet_gem_version }}" != "latest" ]; then
-            export PUPPET_GEM_VERSION='~> {{ puppet_gem_version }}.0'
+            if [ "{{ puppet_gem_version }}" == "5.5" ]; then
+              # Pin to 5.5.6. See PUP-9270 and PUP-9271
+              export PUPPET_GEM_VERSION='{{ puppet_gem_version }}.6'
+            else
+              export PUPPET_GEM_VERSION='~> {{ puppet_gem_version }}.0'
+            fi
           fi
           mkdir .bundled_gems
           export GEM_HOME=`pwd`/.bundled_gems