diff --git a/roll-dep b/roll-dep
index 19ddb8058a..9a14ae45d8 100755
--- a/roll-dep
+++ b/roll-dep
@@ -5,4 +5,17 @@
 
 base_dir=$(dirname "$0")
 
-PYTHONDONTWRITEBYTECODE=1 exec python "$base_dir/roll_dep.py" "$@"
+# Ensure that "depot_tools" is somewhere in PATH so this tool can be used
+# standalone, but allow other PATH manipulations to take priority.
+PATH=$PATH:$base_dir
+
+if [[ $GCLIENT_PY3 = 1 ]]; then
+  # Explicitly run on Python 3
+  PYTHONDONTWRITEBYTECODE=1 exec vpython3 "$base_dir/roll_dep.py" "$@"
+elif [[ $GCLIENT_PY3 = 0 ]]; then
+  # Explicitly run on Python 2
+  PYTHONDONTWRITEBYTECODE=1 exec vpython "$base_dir/roll_dep.py" "$@"
+else
+  # Run on Python 2 for now, allows default to be flipped.
+  PYTHONDONTWRITEBYTECODE=1 exec vpython "$base_dir/roll_dep.py" "$@"
+fi