diff --git a/fetch.bat b/fetch.bat
index 20c4f46aec..6a2e74d210 100755
--- a/fetch.bat
+++ b/fetch.bat
@@ -13,7 +13,12 @@ set PATH=%PATH%;%~dp0
 
 :: Defer control.
 IF "%GCLIENT_PY3%" == "1" (
-  vpython3 "%~dp0\fetch.py" %*
+  :: Explicitly run on Python 3
+  call vpython3 "%~dp0\fetch.py" %*
+) ELSE IF "%GCLIENT_PY3%" == "0" (
+  :: Explicitly run on Python 2
+  call vpython "%~dp0\fetch.py" %*
 ) ELSE (
-  vpython "%~dp0\fetch.py" %*
+  :: Run on Python 2, allows default to be flipped.
+  call vpython "%~dp0\fetch.py" %*
 )
diff --git a/gclient.bat b/gclient.bat
index 39230b3e29..7f72c31dcf 100755
--- a/gclient.bat
+++ b/gclient.bat
@@ -17,8 +17,12 @@ set PATH=%PATH%;%~dp0
 
 :: Defer control.
 IF "%GCLIENT_PY3%" == "1" (
-  :: TODO(1003139): Use vpython3 once vpython3 works on Windows.
-  call python3 "%~dp0gclient.py" %*
+  :: Explicitly run on Python 3
+  call vpython3 "%~dp0gclient.py" %*
+) ELSE IF "%GCLIENT_PY3%" == "0" (
+  :: Explicitly run on Python 2
+  call vpython "%~dp0gclient.py" %*
 ) ELSE (
-  call python "%~dp0gclient.py" %*
+  :: Run on Python 2, allows default to be flipped.
+  call vpython "%~dp0gclient.py" %*
 )
diff --git a/roll-dep.bat b/roll-dep.bat
index c49c88dc51..0295fbd13e 100755
--- a/roll-dep.bat
+++ b/roll-dep.bat
@@ -9,4 +9,13 @@ setlocal
 set PATH=%PATH%;%~dp0
 
 :: Defer control.
-python "%~dp0\roll_dep.py" %*
+IF "%GCLIENT_PY3%" == "1" (
+  :: Explicitly run on Python 3
+  call vpython3 "%~dp0\roll_dep.py" %*
+) ELSE IF "%GCLIENT_PY3%" == "0" (
+  :: Explicitly run on Python 2
+  call vpython "%~dp0\roll_dep.py" %*
+) ELSE (
+  :: Run on Python 2, allows default to be flipped.
+  call vpython "%~dp0\roll_dep.py" %*
+)