diff --git a/Tools/ardupilotwaf/ap_persistent.py b/Tools/ardupilotwaf/ap_persistent.py
new file mode 100644
index 0000000000..7e458456c1
--- /dev/null
+++ b/Tools/ardupilotwaf/ap_persistent.py
@@ -0,0 +1,59 @@
+# Copyright (C) 2016  Intel Corporation. All rights reserved.
+#
+# This file is free software: you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by the
+# Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This file is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+# See the GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program.  If not, see <http://www.gnu.org/licenses/>.
+"""
+Module that changes Waf to keep persistent information across clean operations
+in for performance improvement.
+"""
+from waflib import Build, Task
+
+Build.SAVED_ATTRS.append('ap_persistent_task_sigs')
+Build.SAVED_ATTRS.append('ap_persistent_imp_sigs')
+Build.SAVED_ATTRS.append('ap_persistent_node_deps')
+
+_original_signature = Task.Task.signature
+
+_original_sig_implicit_deps = Task.Task.sig_implicit_deps
+if hasattr(_original_sig_implicit_deps, '__func__'):
+    _original_sig_implicit_deps = _original_sig_implicit_deps.__func__
+
+def _signature(self):
+    s = _original_signature(self)
+    real_fn = self.sig_implicit_deps.__func__
+    if not self.scan or _original_sig_implicit_deps != real_fn:
+        return s
+    bld = self.generator.bld
+    bld.ap_persistent_imp_sigs[self.uid()] = bld.imp_sigs[self.uid()]
+    bld.ap_persistent_node_deps[self.uid()] = bld.node_deps[self.uid()]
+    return s
+Task.Task.signature = _signature
+
+class CleanContext(Build.CleanContext):
+    def clean(self):
+        if not self.options.clean_all_sigs:
+            saved_task_sigs = dict(self.ap_persistent_task_sigs)
+            saved_imp_sigs = dict(self.ap_persistent_imp_sigs)
+            saved_node_deps = dict(self.ap_persistent_node_deps)
+
+        super(CleanContext, self).clean()
+
+        if not self.options.clean_all_sigs:
+            self.task_sigs.update(saved_task_sigs)
+            self.ap_persistent_task_sigs.update(saved_task_sigs)
+
+            self.imp_sigs.update(saved_imp_sigs)
+            self.ap_persistent_imp_sigs.update(saved_imp_sigs)
+
+            self.node_deps.update(saved_node_deps)
+            self.ap_persistent_node_deps.update(saved_node_deps)
diff --git a/Tools/ardupilotwaf/ardupilotwaf.py b/Tools/ardupilotwaf/ardupilotwaf.py
index a03744fd35..fdfac49875 100644
--- a/Tools/ardupilotwaf/ardupilotwaf.py
+++ b/Tools/ardupilotwaf/ardupilotwaf.py
@@ -8,6 +8,8 @@ from waflib.TaskGen import before_method, feature
 import os.path, os
 from collections import OrderedDict
 
+import ap_persistent
+
 SOURCE_EXTS = [
     '*.S',
     '*.c',
@@ -382,25 +384,13 @@ my board".
     g.add_option('--clean-all-sigs',
         action='store_true',
         help='''
-Clean signatures for all tasks. By default, some tasks that don't produce files
-and are time consuming keep their signatures when clean is called without this
-parameter. One example is the group of tasks that check headers included by
-Ardupilot libraries.
+Clean signatures for all tasks. By default, tasks that scan for implicit
+dependencies (like the compilation tasks) keep the dependency information
+across clean commands, so that that information is changed only when really
+necessary. Also, some tasks that don't really produce files persist their
+signature. This option avoids that behavior when cleaning the build.
 ''')
 
 def build(bld):
     bld.add_pre_fun(_process_build_command)
     bld.add_pre_fun(_select_programs_from_group)
-
-class CleanContext(Build.CleanContext):
-    Build.SAVED_ATTRS.append('ap_persistent_task_sigs')
-
-    def clean(self):
-        if not self.options.clean_all_sigs:
-            saved_sigs = dict(self.ap_persistent_task_sigs)
-
-        super(CleanContext, self).clean()
-
-        if not self.options.clean_all_sigs:
-            self.task_sigs.update(saved_sigs)
-            self.ap_persistent_task_sigs.update(saved_sigs)