diff --git a/emsdk.py b/emsdk.py
index d02754f..b07856b 100644
--- a/emsdk.py
+++ b/emsdk.py
@@ -535,11 +535,7 @@ def run(cmd, cwd=None, quiet=False):
 
 
 # http://pythonicprose.blogspot.fi/2009/10/python-extract-targz-archive.html
-def untargz(source_filename, dest_dir, unpack_even_if_exists=False):
-  debug_print('untargz(source_filename=' + source_filename + ', dest_dir=' + dest_dir + ')')
-  if not unpack_even_if_exists and num_files_in_directory(dest_dir) > 0:
-    print("File '" + source_filename + "' has already been unpacked, skipping.")
-    return True
+def untargz(source_filename, dest_dir):
   print("Unpacking '" + source_filename + "' to '" + dest_dir + "'")
   mkdir_p(dest_dir)
   returncode = run(['tar', '-xvf' if VERBOSE else '-xf', sdk_path(source_filename), '--strip', '1'], cwd=dest_dir)
@@ -579,11 +575,7 @@ def move_with_overwrite(src, dest):
 
 
 # http://stackoverflow.com/questions/12886768/simple-way-to-unzip-file-in-python-on-all-oses
-def unzip(source_filename, dest_dir, unpack_even_if_exists=False):
-  debug_print('unzip(source_filename=' + source_filename + ', dest_dir=' + dest_dir + ')')
-  if not unpack_even_if_exists and num_files_in_directory(dest_dir) > 0:
-    print("File '" + source_filename + "' has already been unpacked, skipping.")
-    return True
+def unzip(source_filename, dest_dir):
   print("Unpacking '" + source_filename + "' to '" + dest_dir + "'")
   mkdir_p(dest_dir)
   common_subdir = None
@@ -1552,9 +1544,9 @@ def download_and_unzip(zipfile, dest_dir, download_even_if_exists=False,
   if clobber:
     remove_tree(dest_dir)
   if zipfile.endswith('.zip'):
-    return unzip(download_target, dest_dir, unpack_even_if_exists=True)
+    return unzip(download_target, dest_dir)
   else:
-    return untargz(download_target, dest_dir, unpack_even_if_exists=True)
+    return untargz(download_target, dest_dir)
 
 
 def to_native_path(p):
diff --git a/test/test.py b/test/test.py
index 63db92b..4406e37 100755
--- a/test/test.py
+++ b/test/test.py
@@ -40,11 +40,11 @@ def check_call(cmd, **args):
   subprocess.check_call(cmd, **args)
 
 
-def checked_call_with_output(cmd, expected=None, unexpected=None, stderr=None):
+def checked_call_with_output(cmd, expected=None, unexpected=None, stderr=None, env=None):
   cmd = cmd.split(' ')
   print('running: %s' % cmd)
   try:
-    stdout = subprocess.check_output(cmd, stderr=stderr, universal_newlines=True)
+    stdout = subprocess.check_output(cmd, stderr=stderr, universal_newlines=True, env=env)
   except subprocess.CalledProcessError as e:
     print(e.stderr)
     print(e.stdout)
@@ -272,6 +272,16 @@ int main() {
     run_emsdk('install latest')
     failing_call_with_output(emsdk + ' activate 2.0.1', expected="error: tool is not installed and therefore cannot be activated: 'releases-upstream-13e29bd55185e3c12802bc090b4507901856b2ba-64bit'")
 
+  def test_keep_downloads(self):
+    env = os.environ.copy()
+    env['EMSDK_KEEP_DOWNLOADS'] = '1'
+    # With EMSDK_KEEP_DOWNLOADS the downloading should happen on the first
+    # install of 2.0.28, and again when we install 2.0.29, but not on the
+    # second install of 2.0.28 because the zip should already be local.
+    checked_call_with_output(emsdk + ' install 2.0.28', expected='Downloading:', env=env)
+    checked_call_with_output(emsdk + ' install 2.0.29', expected='Downloading:', env=env)
+    checked_call_with_output(emsdk + ' install 2.0.28', expected='already downloaded, skipping', unexpected='Downloading:', env=env)
+
 
 if __name__ == '__main__':
   unittest.main(verbosity=2)