diff --git a/docker/Dockerfile b/docker/Dockerfile
index 52c7bf560..2c7bafd96 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -8,9 +8,13 @@ LABEL org.opencontainers.image.base.name = "docker.io/library/hpcaitech/cuda-con
 # install torch
 RUN conda install pytorch==1.12.1 torchvision==0.13.1 torchaudio==0.12.1 cudatoolkit=11.3 -c pytorch
 
+# install ninja
+RUN apt-get install -y --no-install-recommends ninja-build
+
 # install apex
 RUN git clone https://github.com/NVIDIA/apex && \
     cd apex && \
+    git checkout 91fcaa && \
     pip install packaging && \
     pip install -v --disable-pip-version-check --no-cache-dir --global-option="--cpp_ext" --global-option="--cuda_ext" --global-option="--fast_layer_norm" ./
 
diff --git a/op_builder/utils.py b/op_builder/utils.py
index 2dbd976fb..cb528eea6 100644
--- a/op_builder/utils.py
+++ b/op_builder/utils.py
@@ -110,7 +110,7 @@ def get_pytorch_version() -> List[int]:
     torch_version = torch.__version__.split('+')[0]
     TORCH_MAJOR = int(torch_version.split('.')[0])
     TORCH_MINOR = int(torch_version.split('.')[1])
-    TORCH_PATCH = int(torch_version.split('.')[2])
+    TORCH_PATCH = int(torch_version.split('.')[2], 16)
     return TORCH_MAJOR, TORCH_MINOR, TORCH_PATCH