diff --git a/INSTALL b/INSTALL
index a294ffe63..ca651e420 100644
--- a/INSTALL
+++ b/INSTALL
@@ -47,7 +47,9 @@ If configure does not work on your system, or if you have a need to
 change configure.ac or Makefile.am, and you have a reasonably
 up-to-date set of tools, running ./autogen.sh in a git clone before
 running ./configure may fix the problem.  To be really sure that you
-aren't using any of the included pre-built scripts, you can do this:
+aren't using any of the included pre-built scripts, especially if you
+are building from a tar distribution instead of a git distribution,
+do this:
 
     ./configure --enable-maintainer-mode
     make maintainer-clean
diff --git a/contrib/intel/INSTALL b/contrib/intel/INSTALL
index aab07ebdd..9b4f9dc01 100644
--- a/contrib/intel/INSTALL
+++ b/contrib/intel/INSTALL
@@ -4,17 +4,23 @@ Copyright (c) 2016 Google, Inc.
 Written by Mike Klein and Matt Sarett
 
 To enable SSE support in libpng, apply intel_sse.patch in your build
-directory.  If you prefer,  manually edit configure.ac and Makefile.am,
-following the instructions below.
+directory, before running "configure".  If you prefer,  manually edit
+configure.ac and Makefile.am, following the instructions below, then
+then follow the instructions in section II of INSTALL in the main libpng
+directory.
 
-Then configure libpng with -DPNG_INTEL_SSE in CPPFLAGS.
-If you only want to optimize 4bpp images, also use -DPNG_NO_INTEL_SSE_3BPP.
+Then configure libpng with -DPNG_INTEL_SSE in CPPFLAGS.  If you only
+want to optimize reading 4bpp images, also use -DPNG_NO_INTEL_SSE_3BPP.
 
 If you have moved intel_init.c and filter_sse2_intrinsics.c to a different
 directory, be sure to update the '#include "../../pngpriv.h"' line in both
 files if necessary to point to the correct relative location of pngpriv.h
 with respect to the new location of those files.
 
+If you are using a custom makefile instead of a configure-generated
+makefile, you will have to update it manually to include contrib/intel/*.c
+and to define PNG_INTEL_SSE and possibly PNG_NO_INTEL_SSE_3BPP.
+
 1. Insert the following lines above the copyright line near the top of
 configure.ac: