diff --git a/ChangeLog b/ChangeLog
index f49af68d..e15feec3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2017-10-10  Even Rouault <even.rouault at spatialys.com>
+
+	* nmake.opt: support a DEBUG=1 option, so as to adjust OPTFLAGS and use
+	/MDd runtime in debug mode.
+
 2017-10-01  Even Rouault <even.rouault at spatialys.com>
 
 	* tools/tiffset.c: fix setting a single value for the ExtraSamples tag
diff --git a/nmake.opt b/nmake.opt
index 74b97007..ec45e779 100644
--- a/nmake.opt
+++ b/nmake.opt
@@ -1,4 +1,4 @@
-# $Id: nmake.opt,v 1.19 2015-08-28 22:19:26 bfriesen Exp $
+# $Id: nmake.opt,v 1.20 2017-10-10 14:39:43 erouault Exp $
 #
 # Copyright (C) 2004, Andrey Kiselev <dron@ak4719.spb.edu>
 #
@@ -24,6 +24,13 @@
 # Compile time parameters for MS Visual C++ compiler.
 # You may edit this file to specify building options.
 
+# Options:
+#    DEBUG - set to disable optimizations and link with debug runtimes
+#
+# Usage examples (see details below):
+# nmake -f makefile.vc
+# nmake -f makefile.vc DEBUG=1
+#
 #
 ###### Edit the following lines to choose a feature set you need. #######
 #
@@ -114,7 +121,11 @@ CHECK_JPEG_YCBCR_SUBSAMPLING = 1
 # with no debugging information.
 # NOTE: /EHsc option required if you want to build the C++ stream API
 #
+!IFDEF DEBUG
+OPTFLAGS =	/MDd /EHsc /W3 /D_CRT_SECURE_NO_DEPRECATE
+!ELSE
 OPTFLAGS =	/Ox /MD /EHsc /W3 /D_CRT_SECURE_NO_DEPRECATE
+!ENDIF
 #OPTFLAGS = 	/Zi 
 
 #