diff --git a/ybd/assembly.py b/ybd/assembly.py
index dd2bf74..22ebb86 100644
--- a/ybd/assembly.py
+++ b/ybd/assembly.py
@@ -127,7 +127,7 @@ def run_build(defs, this):
         sandbox.ldconfig(this)
 
     if this.get('repo'):
-        repos.checkout(this['name'], this['repo'], this['ref'], this['build'])
+        repos.checkout(this)
         this['SOURCE_DATE_EPOCH'] = repos.source_date_epoch(this['build'])
 
     get_build_commands(defs, this)
diff --git a/ybd/cache.py b/ybd/cache.py
index ecfc460..53f1330 100644
--- a/ybd/cache.py
+++ b/ybd/cache.py
@@ -59,7 +59,7 @@ def cache_key(defs, this):
     for factor in definition.get('contents', []):
         hash_factors[factor] = cache_key(defs, factor)
 
-    for factor in ['tree'] + defs.defaults.build_steps:
+    for factor in ['tree', 'submodules'] + defs.defaults.build_steps:
         if definition.get(factor):
             hash_factors[factor] = definition[factor]
 
diff --git a/ybd/repos.py b/ybd/repos.py
index 388ade7..46781b7 100644
--- a/ybd/repos.py
+++ b/ybd/repos.py
@@ -28,7 +28,6 @@
 import utils
 import tempfile
 
-
 if sys.version_info.major == 2:
     # For compatibility with Python 2.
     from ConfigParser import RawConfigParser
@@ -164,7 +163,17 @@ def update_mirror(name, repo, gitdir):
             app.exit(name, 'ERROR: git update mirror failed', repo)
 
 
-def checkout(name, repo, ref, checkout):
+def checkout(this):
+    _checkout(this['name'], this['repo'], this['ref'], this['build'])
+
+    with app.chdir(this['build']):
+        if os.path.exists('.gitmodules') or this.get('submodules'):
+            checkout_submodules(this)
+
+    utils.set_mtime_recursively(this['build'])
+
+
+def _checkout(name, repo, ref, checkout):
     gitdir = os.path.join(app.config['gits'], get_repo_name(repo))
     if not os.path.exists(gitdir):
         mirror(name, repo)
@@ -189,11 +198,6 @@ def checkout(name, repo, ref, checkout):
             app.log(name, 'Git checkout %s in %s' % (repo, checkout))
             app.log(name, 'Upstream version %s' % get_version(checkout, ref))
 
-            if os.path.exists('.gitmodules'):
-                checkout_submodules(name, ref)
-
-    utils.set_mtime_recursively(checkout)
-
 
 def source_date_epoch(checkout):
     with app.chdir(checkout):
@@ -228,8 +232,8 @@ def extract_commit(name, repo, ref, target_dir):
     utils.set_mtime_recursively(target_dir)
 
 
-def checkout_submodules(name, ref):
-    app.log(name, 'Git submodules')
+def checkout_submodules(this):
+    app.log(this, 'Checking git submodules')
     with open('.gitmodules', "r") as gitfile:
         # drop indentation in sections, as RawConfigParser cannot handle it
         content = '\n'.join([l.strip() for l in gitfile.read().splitlines()])
@@ -240,13 +244,18 @@ def checkout_submodules(name, ref):
     for section in parser.sections():
         # validate section name against the 'submodule "foo"' pattern
         submodule = re.sub(r'submodule "(.*)"', r'\1', section)
-        url = parser.get(section, 'url')
         path = parser.get(section, 'path')
+        try:
+            url = this['submodules'][path]['url']
+            app.log(this, 'Processing submodule %s from' % path, url)
+        except:
+            url = parser.get(section, 'url')
+            app.log(this, 'WARNING: fallback to submodule %s from' % path, url)
 
         try:
             # list objects in the parent repo tree to find the commit
             # object that corresponds to the submodule
-            commit = check_output(['git', 'ls-tree', ref, path])
+            commit = check_output(['git', 'ls-tree', this['ref'], path])
 
             # read the commit hash from the output
             fields = commit.split()
@@ -258,11 +267,11 @@ def checkout_submodules(name, ref):
                     raise Exception
 
                 fulldir = os.path.join(os.getcwd(), path)
-                checkout(name, url, submodule_commit, fulldir)
+                _checkout(this['name'], url, submodule_commit, fulldir)
 
             else:
-                app.log(name, 'Skipping submodule %s, not a commit:' % path,
+                app.log(this, 'Skipping submodule %s, not a commit:' % path,
                         fields)
 
         except:
-            app.exit(name, "ERROR: git submodules problem")
+            app.exit(this, "ERROR: git submodules problem", "")