diff --git a/nmake.opt b/nmake.opt
index 79b2fbbb..d9bf15f1 100644
--- a/nmake.opt
+++ b/nmake.opt
@@ -110,12 +110,9 @@ CHECK_JPEG_YCBCR_SUBSAMPLING = 1
 #
 
 
-# Indicate if the compiler provides strtol/strtoul/strtoll/strtoull.
-# Users of MSVC++ 14.0 ("Visual Studio 2015") and later should set all of these to 1
-HAVE_STRTOL = 1
-HAVE_STRTOUL = 1
-HAVE_STRTOLL = 0
-HAVE_STRTOULL = 0
+# Indicate if the compiler provides strtoll/strtoull (default 1)
+# Users of MSVC++ 14.0 ("Visual Studio 2015") and later should set this to 1
+HAVE_STRTOLL = 1
 
 #
 # Pick debug or optimized build flags.  We default to an optimized build
@@ -148,7 +145,7 @@ LD	=	link /nologo
 
 CFLAGS  =	$(OPTFLAGS) $(INCL) $(EXTRAFLAGS)
 CXXFLAGS =	$(OPTFLAGS) $(INCL) $(EXTRAFLAGS)
-EXTRAFLAGS =
+EXTRAFLAGS = -DHAVE_CONFIG_H
 LIBS	=
 
 # Name of the output shared library
diff --git a/port/Makefile.vc b/port/Makefile.vc
index 6122b192..e4471af5 100644
--- a/port/Makefile.vc
+++ b/port/Makefile.vc
@@ -27,30 +27,36 @@
 
 !INCLUDE ..\nmake.opt
 
+HAVE_STRTOL = 1
+HAVE_STRTOUL = 1
+
+# strtoul()/strtoull() are provided together
+!IF $(HAVE_STRTOLL)
+HAVE_STRTOULL = 1
+!ELSE
+HAVE_STRTOULL = 0
+!endif
+
 !IF $(HAVE_STRTOL)
 STRTOL_OBJ =
-EXTRAFLAGS	= -DHAVE_STRTOL $(EXTRAFLAGS)
 !ELSE
 STRTOL_OBJ = strtol.obj
 !ENDIF
 
 !IF $(HAVE_STRTOUL)
 STRTOUL_OBJ =
-EXTRAFLAGS	= -DHAVE_STRTOUL $(EXTRAFLAGS)
 !ELSE
 STRTOUL_OBJ = strtoul.obj
 !ENDIF
 
 !IF $(HAVE_STRTOLL)
 STRTOLL_OBJ =
-EXTRAFLAGS	= -DHAVE_STRTOLL $(EXTRAFLAGS)
 !ELSE
 STRTOLL_OBJ = strtoll.obj
 !ENDIF
 
 !IF $(HAVE_STRTOULL)
 STRTOULL_OBJ =
-EXTRAFLAGS	= -DHAVE_STRTOULL $(EXTRAFLAGS)
 !ELSE
 STRTOULL_OBJ = strtoull.obj
 !ENDIF
diff --git a/port/libport.h b/port/libport.h
index cb302ef4..9f2dace1 100644
--- a/port/libport.h
+++ b/port/libport.h
@@ -24,6 +24,10 @@
 #ifndef _LIBPORT_
 #define	_LIBPORT_
 
+#if defined(HAVE_CONFIG_H)
+#  include <tif_config.h>
+#endif
+
 int getopt(int argc, char * const argv[], const char *optstring);
 extern   char *optarg;
 extern   int opterr;