diff --git a/.appveyor.yml b/.appveyor.yml
index 442abe76e..7bf8cab1b 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -13,7 +13,7 @@ install:
   - conda config --set always_yes yes --set changeps1 no
   - conda update -q conda
   - conda info -a
-  - conda create -q -n test-environment python=%PYTHON_VERSION% numpy scipy scikit-learn pandas joblib pytest
+  - conda create -q -n test-environment python=%PYTHON_VERSION% numpy scipy scikit-learn pandas joblib pygtrie pytest
   - activate test-environment
   - conda install -c conda-forge dlib=19.17
   - pip install imageio
diff --git a/ci/.travis_install.sh b/ci/.travis_install.sh
index 0e3abbfc1..1b28bbfbd 100755
--- a/ci/.travis_install.sh
+++ b/ci/.travis_install.sh
@@ -37,6 +37,7 @@ else
 fi
 
 
+conda install pygtrie
 conda install matplotlib
 conda install jupyter
 conda install pytest
diff --git a/requirements.txt b/requirements.txt
index 773c571bb..22ebb0aa0 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,5 +2,6 @@ scipy>=1.2.1
 numpy>=1.16.2
 pandas>=0.24.2
 scikit-learn>=0.20.3
+pygtrie>=1.0
 matplotlib>=3.0.0
 joblib>=0.13.2
\ No newline at end of file