diff --git a/vpython3 b/vpython3
index 580669a..bc31333 100755
--- a/vpython3
+++ b/vpython3
@@ -34,13 +34,20 @@
 fi
 
 
-MYPATH=$(dirname "${BASH_SOURCE[0]}")
+base_dir=$(dirname "$0")
 
-source "$MYPATH/cipd_bin_setup.sh"
+source "$base_dir/cipd_bin_setup.sh"
 cipd_bin_setup &> /dev/null
 
-base_dir=$(dirname "$0")
-PYTHON3_BIN_RELDIR="$(cat $base_dir/python3_bin_reldir.txt | xargs echo)"
-PATH="$PYTHON3_BIN_RELDIR":"$PYTHON3_BIN_RELDIR/Scripts":"$PATH"
+# If Python bootstrapping is not disabled, make sure Python has been
+# bootstrapped and add it to the front of PATH.
+if [[ $MINGW != 0 && $DEPOT_TOOLS_BOOTSTRAP_PYTHON3 != 0 ]]; then
+  if [[ ! -e $base_dir/python3_bin_reldir.txt ]]; then
+    source "$base_dir/bootstrap_python3"
+    bootstrap_python3
+  fi
+  PYTHON3_BIN_RELDIR="$base_dir/$(cat $base_dir/python3_bin_reldir.txt | xargs echo)"
+  PATH="$PYTHON3_BIN_RELDIR":"$PYTHON3_BIN_RELDIR/Scripts":"$PATH"
+fi
 
-exec "$MYPATH/.cipd_bin/vpython3" "$@"
+exec "$base_dir/.cipd_bin/vpython3" "$@"