diff --git a/CHANGELOG.md b/CHANGELOG.md
index c4fe39ea8..becb52736 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,9 @@ Note that Sockeye has checks in place to not translate with an old model that wa
 
 Each version section may have have subsections for: _Added_, _Changed_, _Removed_, _Deprecated_, and _Fixed_.
 
+## [1.18.28]
+### Changed
+- Temporarily fixing the pyyaml version to 3.12 as version 4.1 introduced some backwards incompatible changes.
 
 ## [1.18.27]
 ### Fixed
diff --git a/requirements/requirements.docs.txt b/requirements/requirements.docs.txt
index 43d5c149c..6ef57dcda 100644
--- a/requirements/requirements.docs.txt
+++ b/requirements/requirements.docs.txt
@@ -2,4 +2,4 @@ sphinx>=1.7.4
 sphinx_rtd_theme
 sphinx-autodoc-typehints>=1.3.0
 recommonmark
-pyyaml
+pyyaml==3.12
diff --git a/requirements/requirements.gpu-cu75.txt b/requirements/requirements.gpu-cu75.txt
index 20650247c..05f69e8f3 100644
--- a/requirements/requirements.gpu-cu75.txt
+++ b/requirements/requirements.gpu-cu75.txt
@@ -1,4 +1,4 @@
-pyyaml
+pyyaml==3.12
 mxnet-cu75mkl==1.2.0
 numpy>=1.12
 typing
diff --git a/requirements/requirements.gpu-cu80.txt b/requirements/requirements.gpu-cu80.txt
index fe96095f5..5371fa344 100644
--- a/requirements/requirements.gpu-cu80.txt
+++ b/requirements/requirements.gpu-cu80.txt
@@ -1,4 +1,4 @@
-pyyaml
+pyyaml==3.12
 mxnet-cu80mkl==1.2.0
 numpy>=1.12
 typing
diff --git a/requirements/requirements.gpu-cu90.txt b/requirements/requirements.gpu-cu90.txt
index 83c71e233..a97c79120 100644
--- a/requirements/requirements.gpu-cu90.txt
+++ b/requirements/requirements.gpu-cu90.txt
@@ -1,4 +1,4 @@
-pyyaml
+pyyaml==3.12
 mxnet-cu90mkl==1.2.0
 numpy>=1.12
 typing
diff --git a/requirements/requirements.gpu-cu91.txt b/requirements/requirements.gpu-cu91.txt
index d9d996cae..ec477e496 100644
--- a/requirements/requirements.gpu-cu91.txt
+++ b/requirements/requirements.gpu-cu91.txt
@@ -1,4 +1,4 @@
-pyyaml
+pyyaml==3.12
 mxnet-cu91mkl==1.2.0
 numpy>=1.12
 typing
diff --git a/requirements/requirements.txt b/requirements/requirements.txt
index bb3697dd0..211846c2c 100644
--- a/requirements/requirements.txt
+++ b/requirements/requirements.txt
@@ -1,4 +1,4 @@
-pyyaml
+pyyaml==3.12
 mxnet-mkl==1.2.0
 numpy>=1.12
 typing
diff --git a/sockeye/__init__.py b/sockeye/__init__.py
index 503e14a61..27876e545 100644
--- a/sockeye/__init__.py
+++ b/sockeye/__init__.py
@@ -11,4 +11,4 @@
 # express or implied. See the License for the specific language governing
 # permissions and limitations under the License.
 
-__version__ = '1.18.27'
+__version__ = '1.18.28'