diff --git a/build.sh b/build.sh
index 322c623..e96ffc4 100755
--- a/build.sh
+++ b/build.sh
@@ -1,6 +1,13 @@
 #!/bin/env bash
 OUTFILE=html/bundle.js
 
+# Check Python version
+pyver=$(python -V | awk '{print $2;}')
+if [[ ! $pyver == 3.7.* ]]; then
+	echo Python 3.7.x is required, got version $pyver
+	exit 1
+fi
+
 # Transcrypt
 transcrypt $@ --nomin pyRCV2.transcrypt || exit 1
 
diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 0000000..e45ba5e
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1,8 @@
+# Dependencies
+Transcrypt==3.7.16
+
+# Dependency tree
+mypy==0.790
+mypy-extensions==0.4.3
+typed-ast==1.4.1
+typing-extensions==3.7.4.3