diff --git a/CHANGES b/CHANGES
index f072808..f12b6dc 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3,7 +3,7 @@ The following are the changes from calc version 2.14.0.11 to date:
     Fixed a number of typos.
 
     Drop support for SunOS, IRIX and MINGW32_NT-5.0 targets.
-    Drop support for CLOCK_SGI_CYCLE.
+    Drop support for CLOCK_SGI_CYCLE.  Drop testing for __MSDOS__.
 
     Minor improvement of various help files.  Made format of help
     files more consistent.
@@ -33,6 +33,10 @@ The following are the changes from calc version 2.14.0.11 to date:
     CALC_CHARBIT.  Added have_limits.h to determine if <limits.h>
     is a system include file.
 
+    Test for _WIN64 when testing for _WIN32.
+
+    Now assuming that <stdio.h> is availabke under _WIN32 and _WIN64.
+
 
 The following are the changes from calc version 2.14.0.9 to 2.14.0.10:
 
diff --git a/alloc.h b/alloc.h
index 11d8dff..1d405ba 100644
--- a/alloc.h
+++ b/alloc.h
@@ -42,9 +42,7 @@
 # include <string.h>
 
 #else
-#if defined(_WIN32) && defined(NOTCYGWIN)
 #include <stdio.h>
-#endif
 
 # if defined(HAVE_NEWSTR)
 E_FUNC void *memcpy();
diff --git a/calc.c b/calc.c
index 71115f8..5ff1d2c 100644
--- a/calc.c
+++ b/calc.c
@@ -29,14 +29,14 @@
 #include <stdio.h>
 #include <signal.h>
 
-#if !defined (_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 # include <pwd.h>
 #endif
 
 #include <sys/types.h>
 #include <ctype.h>
 
-#if defined(_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 # include <io.h>
 # if !defined(NOTCYGWIN)
 /*
@@ -704,7 +704,7 @@ main(int argc, char **argv)
 			if (!p_flag && i_flag && !stdin_tty) {
 				closeinput();
 				if(!freopen("/dev/tty", "r", stdin)) {
-#if defined (_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 					fprintf(stderr,
 						"/dev/tty does not exist on "
 						"this operating system.  "
@@ -734,7 +734,7 @@ main(int argc, char **argv)
 					!p_flag && (!havecommands||i_flag)) {
 				closeinput();
 				if(!freopen("/dev/tty", "r", stdin)) {
-#if defined (_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 					fprintf(stderr,
 						"/dev/tty does not exist on "
 						"this operating system.  "
diff --git a/calc.h b/calc.h
index 0ac7e1a..1a57f3f 100644
--- a/calc.h
+++ b/calc.h
@@ -59,7 +59,7 @@
 #define HOMECHAR	'~'	/* char which indicates home directory */
 #define DOTCHAR		'.'	/* char which indicates current directory */
 #define PATHCHAR	'/'	/* char which separates path components */
-#if defined(__MSDOS__) || defined(__WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 #define LISTCHAR	';'	/* char which separates paths in a list */
 #else
 #define LISTCHAR	':'	/* char which separates paths in a list */
@@ -123,7 +123,7 @@ E_FUNC int get_inode(FILEID id, ZVALUE *ino);
 E_FUNC FILEID reopenid(FILEID id, char *mode, char *name);
 E_FUNC int closeall(void);
 
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 E_FUNC int flushall(void);
 #endif
 
@@ -186,7 +186,7 @@ E_FUNC char *calc_strdup(CONST char *);
  */
 E_FUNC void initialize(void);
 E_FUNC void reinitialize(void);
-#if !defined (_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 E_FUNC int isatty(int tty);	/* TRUE if fd is a tty */
 #endif
 E_FUNC char *version(void);	/* return version string */
diff --git a/codegen.c b/codegen.c
index e005937..0867b1f 100644
--- a/codegen.c
+++ b/codegen.c
@@ -44,9 +44,11 @@
 #include "conf.h"
 #include "strl.h"
 
-#if defined(_WIN32) && !defined(__CYGWIN__)
+#if defined(_WIN32) || defined(_WIN64)
+#if !defined(__CYGWIN__)
 # include <direct.h>
 #endif
+#endif
 
 
 #include "banned.h"	/* include after system header <> includes */
diff --git a/config.c b/config.c
index a3858c6..4c0f1bd 100644
--- a/config.c
+++ b/config.c
@@ -176,7 +176,7 @@ CONFIG oldstd = {	/* backward compatible standard configuration */
 	CTRL_D_VIRGIN_EOF,	/* ^D only exits on virgin lines */
 	NULL,			/* our name */
 	NULL,			/* basename of our name */
-#if defined(_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 	TRUE,			/* running under windows */
 #else
 	FALSE,			/* congrats, you are not using windows */
@@ -236,7 +236,7 @@ CONFIG newstd = {	/* new non-backward compatible configuration */
 	CTRL_D_VIRGIN_EOF,	/* ^D only exits on virgin lines */
 	NULL,			/* our name */
 	NULL,			/* basename of our name */
-#if defined(_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 	TRUE,			/* running under windows */
 #else
 	FALSE,			/* congrats, you are not using windows */
diff --git a/decl.h b/decl.h
index c9eb7b1..6ba4274 100644
--- a/decl.h
+++ b/decl.h
@@ -54,7 +54,7 @@
 /*
  * MS Windows macros
  */
-#elif defined(_WIN32) || defined(WINDOZ)
+#elif defined(_WIN32) || defined(_WIN64)
 
 
   /* determine which type of DLL we must generate */
diff --git a/file.c b/file.c
index bccf41f..f1ee34e 100644
--- a/file.c
+++ b/file.c
@@ -46,7 +46,7 @@
 #include "calcerr.h"
 #include "strl.h"
 
-#if defined(_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 # include <io.h>
 #endif
 
@@ -728,7 +728,7 @@ flushid(FILEID id)
 }
 
 
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 int
 flushall(void)
 {
diff --git a/func.c b/func.c
index 02d8fb5..b0359fe 100644
--- a/func.c
+++ b/func.c
@@ -33,7 +33,7 @@
 #include <errno.h>
 
 
-#if defined(_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 # include <io.h>
 # define _access access
 #endif
@@ -7474,7 +7474,7 @@ f_fflush(int count, VALUE **vals)
 	i = 0;
 	errno = 0;
 	if (count == 0) {
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 		i = flushall();
 #endif /* Windows free systems */
 	} else {
@@ -9043,7 +9043,7 @@ f_system(VALUE *vp)
 	if (conf->calc_debug & CALCDBG_SYSTEM) {
 		printf("%s\n", vp->v_str->s_str);
 	}
-#if defined(_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 	/* if the execute length is 0 then just return 0 */
 	if (vp->v_str->s_len == 0) {
 		result.v_num = itoq((long)0);
@@ -9066,7 +9066,7 @@ f_sleep(int count, VALUE **vals)
 
 	res.v_type = V_NULL;
 	res.v_subtype = V_NOSUBTYPE;
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 	if (count > 0) {
 		if (vals[0]->v_type != V_NUM || qisneg(vals[0]->v_num))
 				return error_value(E_SLEEP);
diff --git a/have_offscl.c b/have_offscl.c
index 7ab331c..105991e 100644
--- a/have_offscl.c
+++ b/have_offscl.c
@@ -69,7 +69,7 @@ main(void)
 	if (value > (off_t)1) {
 		--value;
 	}
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 	if (value <= (off_t)getppid()) {
 		--value;
 	}
diff --git a/have_posscl.c b/have_posscl.c
index b574ac5..798d612 100644
--- a/have_posscl.c
+++ b/have_posscl.c
@@ -69,7 +69,7 @@ main(void)
 	if (value > (FILEPOS)1) {
 		--value;
 	}
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 	if (value <= (FILEPOS)getppid()) {
 		--value;
 	}
diff --git a/help.c b/help.c
index 3f8145f..356b98d 100644
--- a/help.c
+++ b/help.c
@@ -40,7 +40,7 @@
 #include <unistd.h>
 #endif
 
-#if defined(_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 # define popen _popen
 # define pclose _pclose
 #endif
diff --git a/hist.c b/hist.c
index e13ce51..1c2eb61 100644
--- a/hist.c
+++ b/hist.c
@@ -36,7 +36,7 @@
 
 #include <stdio.h>
 #include <ctype.h>
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 # include <pwd.h>
 #endif
 
diff --git a/hist.h b/hist.h
index 411bb39..7965513 100644
--- a/hist.h
+++ b/hist.h
@@ -46,7 +46,7 @@
 #define HOMECHAR	'~'	/* char which indicates home directory */
 #define DOTCHAR		'.'	/* char which indicates current directory */
 #define PATHCHAR	'/'	/* char which separates path components */
-#if defined(__MSDOS__) || defined(__WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 #define LISTCHAR	';'	/* char which separates paths in a list */
 #else
 #define LISTCHAR	':'	/* char which separates paths in a list */
diff --git a/input.c b/input.c
index 162f092..d8f761a 100644
--- a/input.c
+++ b/input.c
@@ -31,7 +31,7 @@
 
 #include <stdio.h>
 #include <ctype.h>
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 # include <pwd.h>
 #else
 # include <stdlib.h>
@@ -407,7 +407,7 @@ f_pathopen(char *name, char *mode, char *pathlist, char **openpath)
 S_FUNC char *
 homeexpand(char *name)
 {
-#if defined(_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 
 	return NULL;
 
@@ -969,12 +969,12 @@ runrcfiles(void)
  * a given device/inode, -1 otherwise.
  *
  *
- * WIN32 NOTE:
+ * _WIN32 and _WIN64 NOTE:
  *
- *	This function does not work under WIN32. The sbuf->st_ino is always
+ *	This function does not work under _WIN32 or _WIN64. The sbuf->st_ino is always
  *	zero because the FAT and NTFS filesystems do not support inodes.
  *	They also don't support links, which is why you need this function
- *	under UNIX. For WIN32, use _fullpath() to determine if you have
+ *	under UNIX. For _WIN32 or _WIN64, use _fullpath() to determine if you have
  *	already opened a file.
  *
  * given:
@@ -994,7 +994,7 @@ isinoderead(struct stat *sbuf)
 
 	/* scan the entire readset */
 	for (i=0; i < maxreadset; ++i) {
-#if defined(_WIN32) || defined(__MSDOS__)
+#if defined(_WIN32) || defined(_WIN64)
 		char tmp[MSDOS_MAX_PATH+1];
 		tmp[MSDOS_MAX_PATH] = '\0';
 		if (_fullpath(tmp, cip->i_name, MSDOS_MAX_PATH) &&
@@ -1120,10 +1120,10 @@ addreadset(char *name, char *path, struct stat *sbuf)
 		return -1;
 	}
 	strlcpy(readset[ret].name, name, name_len+1);
-#if defined(_WIN32) || defined(__MSDOS__)
+#if defined(_WIN32) || defined(_WIN64)
 	/*
-	 * For WIN32, _fullpath expands the path to a fully qualified
-	 * path name, which under WIN32 FAT and NTFS is unique, just
+	 * For _WIN32 or _WIN64, _fullpath expands the path to a fully qualified
+	 * path name, which under _WIN32 or _WIN64 FAT and NTFS is unique, just
 	 * like UNIX inodes. _fullpath also allocated the memory for
 	 * this new longer path name.
 	 */
diff --git a/lib_calc.c b/lib_calc.c
index 84f2ff2..58db95a 100644
--- a/lib_calc.c
+++ b/lib_calc.c
@@ -29,7 +29,7 @@
 #include <setjmp.h>
 #include <signal.h>
 
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 # include <pwd.h>
 #endif
 
@@ -84,7 +84,7 @@ typedef struct {int fd;} ttystruct;
 
 #endif
 
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 # if !defined(USE_SGTTY) && !defined (USE_TERMIOS) && !defined(USE_TERMIO)
 
 -=*#*=- A Windows free system without termio, termios or sgtty!!! -=*#*=-
@@ -240,7 +240,7 @@ libcalc_call_me_first(void)
 	 * Disable SIGPIPE so that the pipe to the help file pager will
 	 * not stop calc.
 	 */
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 	(void) signal(SIGPIPE, SIG_IGN);
 #endif
 
@@ -249,7 +249,7 @@ libcalc_call_me_first(void)
 	 */
 	if (program != NULL) {
 		p = strrchr(program, '/');
-#if defined(_WIN32) || defined(__MSDOS__)
+#if defined(_WIN32) || defined(_WIN64)
 		if (p == NULL) {
 			p = strrchr(program, '\\');
 		}
@@ -481,7 +481,7 @@ cvmalloc_error(char *message)
 S_FUNC void
 initenv(void)
 {
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 	struct passwd *ent;		/* our password entry */
 #endif
 	char *c;
@@ -512,7 +512,7 @@ initenv(void)
 	/* determine the $HOME value */
 	c = (no_env ? NULL : getenv(HOME));
 	home = (c ? strdup(c) : NULL);
-#if defined(_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 	if (home == NULL || home[0] == '\0') {
 		/* free home if it was previously allocated, but empty */
 		if (home != NULL) {
diff --git a/seed.c b/seed.c
index 4809683..5e0546e 100644
--- a/seed.c
+++ b/seed.c
@@ -47,7 +47,7 @@
 #include <unistd.h>
 #endif
 
-#if defined(_WIN32)
+#if defined(_WIN32) || defined(_WIN64)
 # include <process.h>
 # define pid_t int
 #endif
@@ -75,7 +75,7 @@
 #if defined(HAVE_SYS_TIMES_H)
 #include <sys/times.h>
 #endif
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 # include <sys/resource.h>
 #endif
 #if defined(HAVE_STDLIB_H)
@@ -372,7 +372,7 @@ pseudo_seed(void)
 	struct timeval tp;		/* time of day */
 #endif
 	pid_t getpid;			/* process ID */
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
 	pid_t getppid;			/* parent process ID */
 #endif
 #if defined(HAVE_UID_T)
@@ -518,7 +518,7 @@ pseudo_seed(void)
     (void) gettimeofday(&sdata.tp, NULL);
 #endif
     sdata.getpid = getpid();
-#if !defined(_WIN32)
+#if !defined(_WIN32) && !defined(_WIN64)
     sdata.getppid = getppid();
 #endif
 #if defined(HAVE_UID_T)