diff --git a/docker/build_base_image.sh b/docker/build_base_image.sh
index 0c37793a..3b112c30 100755
--- a/docker/build_base_image.sh
+++ b/docker/build_base_image.sh
@@ -3,7 +3,7 @@
 set -x  # Print each script step.
 set -eo pipefail  # Exit the script if any statement returns error.
 
-REAL_PATH=$(python -c "import os,sys;print(os.path.realpath('$0'))")
+REAL_PATH=$(python3 -c "import os,sys;print(os.path.realpath('$0'))")
 cd "$(dirname "$REAL_PATH")/../docker/"
 
 BASE_GIT_COMMIT=$(git rev-parse --verify HEAD)
diff --git a/lower-constraints.txt b/lower-constraints.txt
index 05a8d414..388819de 100644
--- a/lower-constraints.txt
+++ b/lower-constraints.txt
@@ -7,13 +7,13 @@ debtcollector==1.2.0
 docutils==0.11
 extras==1.0.0
 fixtures==3.0.0
-flake8==2.5.5
+flake8==2.6.0
 future==0.16.0
 gevent==1.2.2
 gitdb==0.6.4
 GitPython==1.0.1
 greenlet==0.4.10
-hacking==0.12.0
+hacking==1.1.0
 httplib2==0.9.1
 iso8601==0.1.11
 kazoo==2.2
diff --git a/monasca_common/rest/utils.py b/monasca_common/rest/utils.py
index 13386efc..87888242 100644
--- a/monasca_common/rest/utils.py
+++ b/monasca_common/rest/utils.py
@@ -12,8 +12,9 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import json
+
 import six
-import ujson as json
 
 from monasca_common.rest import exceptions
 
diff --git a/monasca_common/validation/metrics.py b/monasca_common/validation/metrics.py
index e75bc9b4..628823a7 100644
--- a/monasca_common/validation/metrics.py
+++ b/monasca_common/validation/metrics.py
@@ -13,12 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import json
 import math
 import re
+import sys
 
 import six
-import sys
-import ujson
 
 # This is used to ensure that metrics with a timestamp older than
 # RECENT_POINT_THRESHOLD_DEFAULT seconds (or the value passed in to
@@ -108,7 +108,7 @@ def validate_value_meta(value_meta):
             raise InvalidValueMeta(msg)
 
     try:
-        value_meta_json = ujson.dumps(value_meta)
+        value_meta_json = json.dumps(value_meta)
     except Exception:
         raise InvalidValueMeta("Unable to serialize valueMeta into JSON")
     if len(value_meta_json) > VALUE_META_VALUE_MAX_LENGTH:
diff --git a/requirements.txt b/requirements.txt
index 6808390e..7e7ba7b2 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -8,5 +8,4 @@ oslo.config>=5.2.0 # Apache-2.0
 oslo.policy>=1.30.0 # Apache-2.0
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 pyparsing>=2.1.0 # MIT
-ujson>=1.35 # BSD
 confluent-kafka>=0.11.4 # Apache-2.0
diff --git a/test-requirements.txt b/test-requirements.txt
index a74545d1..d739bf3f 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -2,7 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 # Hacking already pins down pep8, pyflakes and flake8
-bandit!=1.6.0,>=1.1.0 # Apache-2.0
+bandit!=1.6.0,>=1.1.0,<=1.6.2
 hacking>=1.1.0,<1.2.0 # Apache-2.0
 Babel!=2.4.0,>=2.3.4 # BSD
 coverage!=4.4,>=4.0 # Apache-2.0