diff --git a/m4/check-cflags.m4 b/m4/check-cflags.m4
index e02b8340..31e36c67 100644
--- a/m4/check-cflags.m4
+++ b/m4/check-cflags.m4
@@ -1,3 +1,7 @@
+dnl
+dnl This file contains code derived from WINE_TRY_CFLAGS() and is used courtesy of Alexandre Julliard.
+dnl
+
 dnl VKD3D_CHECK_CFLAGS(flags)
 AC_DEFUN([VKD3D_CHECK_CFLAGS],
   [AS_VAR_PUSHDEF([vkd3d_cflags], vkd3d_cv_cflags_[[$1]])dnl
diff --git a/m4/check-mingw-prog.m4 b/m4/check-mingw-prog.m4
index d0137ebe..ac3e07d3 100644
--- a/m4/check-mingw-prog.m4
+++ b/m4/check-mingw-prog.m4
@@ -1,3 +1,7 @@
+dnl
+dnl This file contains code derived from WINE_CHECK_MINGW_PROG() and is used courtesy of Alexandre Julliard.
+dnl
+
 dnl VKD3D_CHECK_MINGW32_PROG(cc-variable, crosstarget-variable, [value-if-not-found], [path])
 AC_DEFUN([VKD3D_CHECK_MINGW32_PROG],
 [AC_SUBST([$2], [$3])