diff --git a/project/headers.mk b/project/headers.mk
index 9d50ee3..065fb10 100644
--- a/project/headers.mk
+++ b/project/headers.mk
@@ -1,5 +1,11 @@
-API_HEADERS = \
+api_include_dirs    = $(PROJECT_DIR)/include/cparser/*/
+api_include_headers = $(addsuffix *.h,$(api_include_dirs))
+api_sort_headers    = $(sort $(wildcard $(api_include_headers)))
+API_HEADERS         = $(api_sort_headers)
 
-INTERNAL_HEADERS = \
+internal_dirs       = $(PROJECT_DIR)/src/internal/
+internal_files      = $(addsuffix *.h,$(internal_dirs))
+internal_sort_files = $(sort $(wildcard $(internal_files)))
+INTERNAL_HEADERS    = $(subst $(PROJECT_DIR)/src/,src/,$(internal_sort_files))
 
-ALL_HEADERS = $(API_HEADERS) $(INTERNAL_HEADERS)
+ALL_HEADERS         = $(API_HEADERS) $(INTERNAL_HEADERS)