--- a/build/subconfigure.py
+++ b/build/subconfigure.py
@@ -238,19 +238,32 @@ def prepare(srcdir, objdir, shell, args)
     with open(data_file, 'wb') as f:
         pickle.dump(data, f)
 
 
 def prefix_lines(text, prefix):
     return ''.join('%s> %s' % (prefix, line) for line in text.splitlines(True))
 
 
+def execute_and_prefix(*args, **kwargs):
+    prefix = kwargs['prefix']
+    del kwargs['prefix']
+    proc = subprocess.Popen(*args, stdout=subprocess.PIPE,
+                            stderr=subprocess.STDOUT, **kwargs)
+    while True:
+        line = proc.stdout.readline()
+        if not line:
+            break
+        print prefix_lines(line.rstrip(), prefix)
+        sys.stdout.flush()
+    return proc.wait()
+
+
 def run(objdir):
     ret = 0
-    output = ''
 
     with open(os.path.join(objdir, CONFIGURE_DATA), 'rb') as f:
         data = pickle.load(f)
 
     data['objdir'] = objdir
     relobjdir = data['relobjdir'] = os.path.relpath(objdir, os.getcwd())
 
     cache_file = data['cache-file']
@@ -315,21 +328,20 @@ def run(objdir):
 
         # Pass --no-create to configure so that it doesn't run config.status.
         # We're going to run it ourselves.
         command += ['--no-create']
 
         print prefix_lines('configuring', relobjdir)
         print prefix_lines('running %s' % ' '.join(command[:-1]), relobjdir)
         sys.stdout.flush()
-        try:
-            output += subprocess.check_output(command,
-                stderr=subprocess.STDOUT, cwd=objdir, env=data['env'])
-        except subprocess.CalledProcessError as e:
-            return relobjdir, e.returncode, e.output
+        returncode = execute_and_prefix(command, cwd=objdir, env=data['env'],
+                                        prefix=relobjdir)
+        if returncode:
+            return returncode
 
         # Leave config.status with a new timestamp if configure is newer than
         # its original mtime.
         if config_status and os.path.getmtime(configure) <= config_status.mtime:
             config_status.update_time()
 
     # Only run config.status if one of the following is true:
     # - config.status changed or did not exist
@@ -353,28 +365,23 @@ def run(objdir):
             if not os.path.exists(t) or \
                     os.path.getmtime(f) < os.path.getmtime(t):
                 skip_config_status = False
 
     if not skip_config_status:
         if skip_configure:
             print prefix_lines('running config.status', relobjdir)
             sys.stdout.flush()
-        try:
-            output += subprocess.check_output([data['shell'], '-c',
-                './config.status'], stderr=subprocess.STDOUT, cwd=objdir,
-                env=data['env'])
-        except subprocess.CalledProcessError as e:
-            ret = e.returncode
-            output += e.output
+        ret = execute_and_prefix([data['shell'], '-c', './config.status'],
+                                 cwd=objdir, env=data['env'], prefix=relobjdir)
 
         for f in contents:
             f.update_time()
 
-    return relobjdir, ret, output
+    return ret
 
 
 def subconfigure(args):
     parser = argparse.ArgumentParser()
     parser.add_argument('--list', type=str,
         help='File containing a list of subconfigures to run')
     parser.add_argument('--skip', type=str,
         help='File containing a list of Subconfigures to skip')
@@ -388,19 +395,17 @@ def subconfigure(args):
         skips = set(open(args.skip, 'rb').read().splitlines())
         subconfigures = [s for s in subconfigures if s not in skips]
 
     if not subconfigures:
         return 0
 
     ret = 0
     for subconfigure in subconfigures:
-        relobjdir, returncode, output = run(subconfigure)
-        print prefix_lines(output, relobjdir)
-        sys.stdout.flush()
+        returncode = run(subconfigure)
         ret = max(returncode, ret)
         if ret:
             break
     return ret
 
 
 def main(args):
     if args[0] != '--prepare':