diff --git a/Tools/ardupilotwaf/ap_library.py b/Tools/ardupilotwaf/ap_library.py
index 67cb614282..1dc690fece 100644
--- a/Tools/ardupilotwaf/ap_library.py
+++ b/Tools/ardupilotwaf/ap_library.py
@@ -206,6 +206,8 @@ class ap_library_check_headers(Task.Task):
 
         # force dependency scan, if necessary
         self.compiled_task.signature()
+        if not self.compiled_task.uid() in self.generator.bld.node_deps:
+            return r, []
         for n in self.generator.bld.node_deps[self.compiled_task.uid()]:
             # using common Node methods doesn't work here
             p = n.abspath()
diff --git a/Tools/ardupilotwaf/chibios.py b/Tools/ardupilotwaf/chibios.py
index 532e75a4b3..26b8c0e313 100644
--- a/Tools/ardupilotwaf/chibios.py
+++ b/Tools/ardupilotwaf/chibios.py
@@ -19,7 +19,11 @@ import subprocess
 _dynamic_env_data = {}
 def _load_dynamic_env_data(bld):
     bldnode = bld.bldnode.make_node('modules/ChibiOS')
-    tmp_str = bldnode.find_node('include_dirs').read()
+    include_dirs_node = bldnode.find_node('include_dirs')
+    if include_dirs_node is None:
+        _dynamic_env_data['include_dirs'] = []
+        return
+    tmp_str = include_dirs_node.read()
     tmp_str = tmp_str.replace(';\n','')
     tmp_str = tmp_str.replace('-I','')  #remove existing -I flags
     # split, coping with separator
diff --git a/Tools/ardupilotwaf/git_submodule.py b/Tools/ardupilotwaf/git_submodule.py
index be28216e9c..e2c727e05b 100644
--- a/Tools/ardupilotwaf/git_submodule.py
+++ b/Tools/ardupilotwaf/git_submodule.py
@@ -91,7 +91,7 @@ class update_submodule(Task.Task):
                 else:
                     r = Task.RUN_ME
 
-        if self.non_fast_forward:
+        if getattr(self,'non_fast_forward',[]):
             r = Task.SKIP_ME
 
         return r
@@ -148,7 +148,7 @@ def git_submodule(bld, git_submodule, **kw):
 def _post_fun(bld):
     Logs.info('')
     for name, t in _submodules_tasks.items():
-        if not t.non_fast_forward:
+        if not getattr(t,'non_fast_forward',[]):
             continue
         Logs.warn("Submodule %s not updated: non-fastforward" % name)
 
diff --git a/wscript b/wscript
index 820b566ddc..0517655459 100644
--- a/wscript
+++ b/wscript
@@ -528,7 +528,6 @@ def configure(cfg):
     cfg.msg('Setting board to', cfg.options.board)
     cfg.get_board().configure(cfg)
 
-    cfg.load('clang_compilation_database')
     cfg.load('waf_unit_test')
     cfg.load('mavgen')
     cfg.load('dronecangen')