diff --git a/build/moz.configure/util.configure b/build/moz.configure/util.configure
index 27637fa29921..a4ddf4f498cf 100644
--- a/build/moz.configure/util.configure
+++ b/build/moz.configure/util.configure
@@ -162,12 +162,10 @@ normalize_path = normalize_path()
 # exists.
 # The `paths` parameter may be passed to search the given paths instead of
 # $PATH.
-@imports(_from='which', _import='which')
-@imports(_from='which', _import='WhichError')
-@imports('itertools')
 @imports('sys')
 @imports(_from='os', _import='pathsep')
 @imports(_from='os', _import='environ')
+@imports(_from='mozfile', _import='which')
 def find_program(file, paths=None):
     # The following snippet comes from `which` itself, with a slight
     # modification to use lowercase extensions, because it's confusing rustup
@@ -184,21 +182,18 @@ def find_program(file, paths=None):
     else:
         exts = None
 
-    try:
-        if is_absolute_or_relative(file):
-            return normalize_path(which(os.path.basename(file),
-                                        [os.path.dirname(file)], exts=exts))
-        if paths:
-            if not isinstance(paths, (list, tuple)):
-                die("Paths provided to find_program must be a list of strings, "
-                    "not %r", paths)
-            paths = list(itertools.chain(
-                *(p.split(pathsep) for p in paths if p)))
-        else:
-            paths = environ['PATH'].split(pathsep)
-        return normalize_path(which(file, path=paths, exts=exts))
-    except WhichError:
-        return None
+    if is_absolute_or_relative(file):
+        path = which(os.path.basename(file), path=os.path.dirname(file), exts=exts)
+        return normalize_path(path) if path else None
+
+    if paths:
+        if not isinstance(paths, (list, tuple)):
+            die("Paths provided to find_program must be a list of strings, "
+                "not %r", paths)
+        paths = pathsep.join(paths)
+
+    path = which(file, path=paths, exts=exts)
+    return normalize_path(path) if path else None
 
 
 @imports('os')
diff --git a/python/mozbuild/mozbuild/test/configure/common.py b/python/mozbuild/mozbuild/test/configure/common.py
index 97760b0b958a..e43daffba8a1 100644
--- a/python/mozbuild/mozbuild/test/configure/common.py
+++ b/python/mozbuild/mozbuild/test/configure/common.py
@@ -11,13 +11,12 @@ import subprocess
 import sys
 import tempfile
 import unittest
+from StringIO import StringIO
 
 from mozbuild.configure import ConfigureSandbox
 from mozbuild.util import ReadOnlyNamespace
 from mozpack import path as mozpath
-
-from StringIO import StringIO
-from which import WhichError
+from six import string_types
 
 from buildconfig import (
     topobjdir,
@@ -110,13 +109,12 @@ class ConfigureTestSandbox(ConfigureSandbox):
         if what in self.modules:
             return self.modules[what]
 
-        if what == 'which.which':
+        if what == 'mozfile.which':
             return self.which
 
-        if what == 'which':
+        if what == 'mozfile':
             return ReadOnlyNamespace(
                 which=self.which,
-                WhichError=WhichError,
             )
 
         if what == 'subprocess.Popen':
@@ -186,18 +184,20 @@ class ConfigureTestSandbox(ConfigureSandbox):
         path_out.value = fake_short_path(path_in)
         return length
 
-    def which(self, command, path=None, exts=None):
+    def which(self, command, mode=None, path=None, exts=None):
+        if isinstance(path, string_types):
+            path = path.split(os.pathsep)
+
         for parent in (path or self._search_path):
             c = mozpath.abspath(mozpath.join(parent, command))
             for candidate in (c, ensure_exe_extension(c)):
                 if self.imported_os.path.exists(candidate):
                     return candidate
-        raise WhichError()
+        return None
 
     def Popen(self, args, stdin=None, stdout=None, stderr=None, **kargs):
-        try:
-            program = self.which(args[0])
-        except WhichError:
+        program = self.which(args[0])
+        if not program:
             raise OSError(errno.ENOENT, 'File not found')
 
         func = self._subprocess_paths.get(program)