diff --git a/Makefile.inc b/Makefile.inc
index 529250d9b9..2b62e785f1 100644
--- a/Makefile.inc
+++ b/Makefile.inc
@@ -88,7 +88,7 @@ $(spc) +=
 files-in-dir-recursive=$(filter $(1)%,$(2))
 
 # parent-dir,dir/
-parent-dir=$(dir $(subst $( ),/,$(strip $(subst /, ,$(1)))))
+parent-dir=$(dir $(if $(patsubst /%,,$(1)),,/)$(subst $( ),/,$(strip $(subst /, ,$(1)))))
 
 # filters out exactly the directory specified
 # filter-out-dir,dir_to_keep,dirs
@@ -96,13 +96,13 @@ filter-out-dir=$(filter-out $(1),$(2))
 
 # filters out dir_to_keep and all its parents
 # filter-out-dirs,dir_to_keep,dirs
-filter-out-dirs=$(if $(filter-out ./,$(1)),$(call filter-out-dirs,$(call parent-dir,$(1)),$(call filter-out-dir,$(1),$(2))),$(call filter-out-dir,$(1),$(2)))
+filter-out-dirs=$(if $(filter-out ./ /,$(1)),$(call filter-out-dirs,$(call parent-dir,$(1)),$(call filter-out-dir,$(1),$(2))),$(call filter-out-dir,$(1),$(2)))
 
 # dir-wildcards,dirs
 dir-wildcards=$(addsuffix %,$(1))
 
 # files-in-dir,dir,files
-files-in-dir=$(filter-out $(call dir-wildcards,$(call filter-out-dirs,$(1),$(dir $(2)))),$(call files-in-dir-recursive,$(1),$(2)))
+files-in-dir=$(filter-out $(call dir-wildcards,$(call filter-out-dirs,$(1),$(sort $(dir $(2))))),$(call files-in-dir-recursive,$(1),$(2)))
 
 #######################################################################
 # reduce command line length by linking the objects of each