diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 1bbda7b..751b65e 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -21,7 +21,8 @@ jobs:
     - name: build new conda env
       run: |
         eval "$(conda shell.bash hook)"
-        conda create -p ./env -y python=${{ matrix.python-version }} --file test-requirements.txt --channel conda-forge --channel bioconda
+        conda install -n base mamba -y --channel conda-forge
+        mamba create -p ./env -y python=${{ matrix.python-version }} --file test-requirements.txt --channel conda-forge --channel bioconda
         conda activate ./env
         pip install -e .
 
diff --git a/test-requirements.txt b/test-requirements.txt
index 209de25..e8e1d90 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -5,7 +5,7 @@ pybedtools
 pytest
 sphinx>4
 pygments
-sphinx_rtd_theme
+sphinx_rtd_theme>=1.2.2
 ucsc-bedgraphtobigwig
 ucsc-fatotwobit
 ucsc-bedtobigbed
diff --git a/trackhub/trackhub_from_excel b/trackhub/trackhub_from_excel
index 72814f8..eeb3213 100755
--- a/trackhub/trackhub_from_excel
+++ b/trackhub/trackhub_from_excel
@@ -590,7 +590,7 @@ def create_example(filename):
     # In Python >=3.9, importlib.resources.files would work, but the method
     # used here is agnostic to Python versions.
     example_file = os.path.join(
-        os.path.dirname(sys.modules['trackhub'].__file),
+        os.path.dirname(sys.modules['trackhub'].__file__),
         "example.xlsx"
     )
     wb = load_workbook(example_file, data_only=True)