diff --git a/modules/src/system/build.lua b/modules/src/system/build.lua
index b2cbd71f6..4c2b8e52d 100644
--- a/modules/src/system/build.lua
+++ b/modules/src/system/build.lua
@@ -10,6 +10,7 @@ clibrary {
 		"./write.c",
 		"./syssystem.c",
 		"./strndup.c",
+		"./setbinarymode.c",
 	},
 	hdrs = { "./system.h" },
 }
diff --git a/modules/src/system/setbinarymode.c b/modules/src/system/setbinarymode.c
new file mode 100644
index 000000000..8a6408e6a
--- /dev/null
+++ b/modules/src/system/setbinarymode.c
@@ -0,0 +1,14 @@
+#include "system.h"
+#include <fcntl.h>
+
+#if defined WIN32
+#include <io.h>
+#endif
+
+void sys_setbinarymode(FILE* fp)
+{
+    #if defined WIN32
+        setmode(fileno(fp), O_BINARY);
+    #endif
+}
+
diff --git a/modules/src/system/system.h b/modules/src/system/system.h
index 2489c1f03..582dd44e9 100644
--- a/modules/src/system/system.h
+++ b/modules/src/system/system.h
@@ -89,4 +89,8 @@ char* sys_tmpnam(char *buffer);
 extern char* strndup(const char* s, size_t n);
 #endif
 
+/* Sets stdin, stdout or stderr to binary mode --- required on Windows, noop on
+ * sane systems. */
+extern void sys_setbinarymode(FILE* fp);
+
 #endif /* __SYSTEM_INCLUDED__ */
diff --git a/util/ego/build.lua b/util/ego/build.lua
index 51c57d7fc..8fbf43bca 100644
--- a/util/ego/build.lua
+++ b/util/ego/build.lua
@@ -40,6 +40,7 @@ cprogram {
 		"./ca/ca_put.h",
 		"util/ego/share+lib",
 		"modules/src/em_data+lib",
+		"modules/src/system+lib",
 		"h+emheaders",
 	},
 	vars = {
diff --git a/util/ego/ca/ca.c b/util/ego/ca/ca.c
index 1bf73d24a..5f50d8ddd 100644
--- a/util/ego/ca/ca.c
+++ b/util/ego/ca/ca.c
@@ -13,6 +13,7 @@
 #include <string.h>
 #include <em_pseu.h>
 #include <em_mes.h>
+#include "system.h"
 #include "../share/types.h"
 #include "ca.h"
 #include "../share/debug.h"
@@ -257,15 +258,16 @@ char* argv[];
 	fproc = getptable(pname_in); /* proc table */
 	fdblock = getdtable(dname_in); /* data block table */
 	dlength = makedmap(fdblock); /* allocate dmap table */
-	df = openfile(dname_out, "r");
+	df = openfile(dname_out, "rb");
 	getdnames(df);
 	fclose(df);
-	pf = openfile(pname_out, "r");
+	pf = openfile(pname_out, "rb");
 	getpnames(pf);
 	fclose(pf);
 	uniq_names();
-	f = openfile(lname_in, "r");
+	f = openfile(lname_in, "rb");
 	f2 = stdout;
+	sys_setbinarymode(f2);
 	cputmagic(f2); /* write magic number */
 	while ((lnp = get_ca_lines(f, &curproc)) != (line_p)0)
 	{
diff --git a/util/ego/cf/cf.c b/util/ego/cf/cf.c
index 6ee94af46..1f10e24ed 100644
--- a/util/ego/cf/cf.c
+++ b/util/ego/cf/cf.c
@@ -557,15 +557,15 @@ char* argv[];
 	fdblock = getdtable(dname_in); /* data block table */
 	lpi_set = Cempty_set(plength);
 	cai_set = Cempty_set(plength);
-	if ((f = fopen(lname_in, "r")) == NULL)
+	if ((f = fopen(lname_in, "rb")) == NULL)
 	{
 		error("cannot open %s", lname_in);
 	}
-	if ((f2 = fopen(lname_out, "w")) == NULL)
+	if ((f2 = fopen(lname_out, "wb")) == NULL)
 	{
 		error("cannot open %s", lname_out);
 	}
-	if ((gf2 = fopen(bname_out, "w")) == NULL)
+	if ((gf2 = fopen(bname_out, "wb")) == NULL)
 	{
 		error("cannot open %s", bname_out);
 	}
@@ -603,12 +603,12 @@ char* argv[];
 	/* Compute transitive closure of used/changed
 	 * variables information for every procedure.
 	 */
-	if ((f = fopen(dname_out, "w")) == NULL)
+	if ((f = fopen(dname_out, "wb")) == NULL)
 	{
 		error("cannot open %s", dname_out);
 	}
 	putdtable(fdblock, f);
-	if ((f = fopen(pname_out, "w")) == NULL)
+	if ((f = fopen(pname_out, "wb")) == NULL)
 	{
 		error("cannot open %s", pname_out);
 	}
diff --git a/util/ego/ic/ic.c b/util/ego/ic/ic.c
index a0203aefb..af0907bac 100644
--- a/util/ego/ic/ic.c
+++ b/util/ego/ic/ic.c
@@ -83,9 +83,9 @@ char* argv[];
 	const char* dname_out = argv[6];
 	const char* lname_out = argv[7];
 
-	FILE* lfile = openfile(lname_out, "w");
-	FILE* pdump = openfile(pdump_out, "w");
-	FILE* ddump = openfile(ddump_out, "w");
+	FILE* lfile = openfile(lname_out, "wb");
+	FILE* pdump = openfile(pdump_out, "wb");
+	FILE* ddump = openfile(ddump_out, "wb");
 
 	FILE* dfile;
 	FILE* pfile;
@@ -117,9 +117,9 @@ char* argv[];
 	cleanprocs(prochash, NPROCHASH, 0);
 	cleandblocks(symhash, NSYMHASH, 0);
 	/* Now write the datablock table and the proctable */
-	dfile = openfile(dname_out, "w");
+	dfile = openfile(dname_out, "wb");
 	putdtable(fdblock, dfile);
-	pfile = openfile(pname_out, "w");
+	pfile = openfile(pname_out, "wb");
 	putptable(fproc, pfile, FALSE);
 	exit(0);
 }
diff --git a/util/ego/ic/ic_lib.c b/util/ego/ic/ic_lib.c
index 3933493e8..b2bf800e1 100644
--- a/util/ego/ic/ic_lib.c
+++ b/util/ego/ic/ic_lib.c
@@ -298,7 +298,7 @@ char* argv[];
 				return NULL;
 			}
 			filename = argv[argcnt];
-			if ((curfile = fopen(filename, "r")) == NULL)
+			if ((curfile = fopen(filename, "rb")) == NULL)
 			{
 				error("cannot open %s", filename);
 			}
diff --git a/util/ego/il/il.c b/util/ego/il/il.c
index 6fd30dca9..1f3455538 100644
--- a/util/ego/il/il.c
+++ b/util/ego/il/il.c
@@ -71,10 +71,10 @@ STATIC void pass1(const char *lnam, const char *bnam, const char *cnam)
 	short kind;
 	line_p l;
 
-	f = openfile(lnam, "r");
-	gf = openfile(bnam, "r");
-	cf = openfile(cnam, "w");
-	ccf = openfile(ccname, "w");
+	f = openfile(lnam, "rb");
+	gf = openfile(bnam, "rb");
+	cf = openfile(cnam, "wb");
+	ccf = openfile(ccname, "wb");
 	mesregs = Lempty_set();
 	apriori(fproc);
 	/* use information from the procedure table to
@@ -132,9 +132,9 @@ STATIC void pass2(const char *cnam, long space)
 	FILE* cf, *cf2, *ccf;
 	call_p c, a;
 
-	cf = openfile(cnam, "r");
-	cf2 = openfile(cname2, "w");
-	ccf = openfile(ccname, "r");
+	cf = openfile(cnam, "rb");
+	cf2 = openfile(cname2, "wb");
+	ccf = openfile(ccname, "rb");
 	while ((c = getcall(cf)) != (call_p)0)
 	{
 		/* process all calls */
@@ -161,7 +161,7 @@ STATIC void pass2(const char *cnam, long space)
 	fclose(ccf);
 	if (!kp_temps)
 		unlink(ccname);
-	cf2 = openfile(cname2, "r");
+	cf2 = openfile(cname2, "rb");
 	add_actuals(fproc, cf2);
 	cleancals(fproc); /* remove calls that were not selected */
 	/* add actual parameters to each selected call */
@@ -186,12 +186,12 @@ void pass3(const char *lnam, const char *lnam2)
 	line_p l, startscan, cal;
 	short lastcid; /* last call-id seen */
 
-	lfile = openfile(lnam, "r");
-	lfilerand = openfile(lnam, "r");
-	lfile2 = openfile(lnam2, "w");
+	lfile = openfile(lnam, "rb");
+	lfilerand = openfile(lnam, "rb");
+	lfile2 = openfile(lnam2, "wb");
 	if (verbose)
 	{
-		sfile = openfile(sname, "w");
+		sfile = openfile(sname, "wb");
 	}
 	mesregs = Lempty_set();
 	while ((l = get_text(lfile, &curproc)) != (line_p)0)
@@ -356,10 +356,10 @@ char* argv[];
 	space = total_size * space / 100;
 	pass2(cname, space); /* select calls to be expanded */
 	pass3(files->lname_in, files->lname_out); /* do substitutions */
-	f = openfile(files->dname_out, "w");
+	f = openfile(files->dname_out, "wb");
 	il_cleanptab(fproc); /* remove extended data structures */
 	putdtable(fdblock, f);
-	f = openfile(files->pname_out, "w");
+	f = openfile(files->pname_out, "wb");
 	putptable(fproc, f, FALSE);
 	report("inline substitutions", Ssubst);
 #ifdef VERBOSE
diff --git a/util/ego/ra/makeitems.c b/util/ego/ra/makeitems.c
index f8bc64989..8be973b99 100644
--- a/util/ego/ra/makeitems.c
+++ b/util/ego/ra/makeitems.c
@@ -69,10 +69,10 @@ int main(int argc, char *argv[])
 	if (argc != 3) {
 		error("usage: makeitems mnemfile itemfile");
 	}
-	if ((f1 = fopen(argv[1],"r")) == NULL) {
+	if ((f1 = fopen(argv[1],"rb")) == NULL) {
 		error("cannot open mnemonic file");
 	}
-	if ((f2 = fopen(argv[2],"r")) == NULL) {
+	if ((f2 = fopen(argv[2],"rb")) == NULL) {
 		error("cannot open item file");
 	}
 	convert(f1,f2);
diff --git a/util/ego/share/get.c b/util/ego/share/get.c
index 84a805828..16a88286e 100644
--- a/util/ego/share/get.c
+++ b/util/ego/share/get.c
@@ -167,7 +167,7 @@ proc_p getptable(const char *pname)
 	proc_p head, p, *pp;
 	short all;
 
-	if ((curinp = fopen(pname,"r")) == NULL) {
+	if ((curinp = fopen(pname,"rb")) == NULL) {
 		error("cannot open %s",pname);
 	}
 
@@ -234,7 +234,7 @@ dblock_p getdtable(const char *dname)
 	int n;
 
 	head = (dblock_p) 0;
-	if ((curinp = fopen(dname,"r")) == NULL) {
+	if ((curinp = fopen(dname,"rb")) == NULL) {
 		error("cannot open %s", dname);
 	}
 	olength = getshort();
diff --git a/util/ego/share/go.c b/util/ego/share/go.c
index 0ccd3c6e9..477d54dea 100644
--- a/util/ego/share/go.c
+++ b/util/ego/share/go.c
@@ -33,7 +33,7 @@ STATIC void mach_init(char* machfile, void (*phase_machinit)(void *))
 
 	FILE* f;
 
-	f = openfile(machfile, "r");
+	f = openfile(machfile, "rb");
 	fscanf(f, "%d", &ws);
 	fscanf(f, "%d", &ps);
 	if (ws != ps && ps != 2 * ws)
@@ -104,10 +104,10 @@ void go(int argc, char * const *argv,
 	(*initialize)(NULL);
 	if (optimize == no_action)
 		return;
-	f = openfile(files->lname_in, "r");
-	gf = openfile(files->bname_in, "r");
-	f2 = openfile(files->lname_out, "w");
-	gf2 = openfile(files->bname_out, "w");
+	f = openfile(files->lname_in, "rb");
+	gf = openfile(files->bname_in, "rb");
+	f2 = openfile(files->lname_out, "wb");
+	gf2 = openfile(files->bname_out, "wb");
 	mesregs = Lempty_set();
 	while (getunit(gf, f, &kind, &g, &l, &curproc, TRUE))
 	{
@@ -135,10 +135,10 @@ void go(int argc, char * const *argv,
 	fclose(f2);
 	fclose(gf);
 	fclose(gf2);
-	f = openfile(files->dname_out, "w");
+	f = openfile(files->dname_out, "wb");
 	putdtable(fdblock, f);
 	/* fclose(f); done by putdtable */
-	f = openfile(files->pname_out, "w");
+	f = openfile(files->pname_out, "wb");
 	putptable(fproc, f, TRUE);
 	/* fclose(f); done by putptable */
 	core_usage();
diff --git a/util/ego/share/makecldef.c b/util/ego/share/makecldef.c
index ac831ed3b..5358809c4 100644
--- a/util/ego/share/makecldef.c
+++ b/util/ego/share/makecldef.c
@@ -75,10 +75,10 @@ int main(int argc, char *argv[])
 	if (argc != 3) {
 		error("usage: makeclassdef mnemfile classfile");
 	}
-	if ((f1 = fopen(argv[1],"r")) == NULL) {
+	if ((f1 = fopen(argv[1],"rb")) == NULL) {
 		error("cannot open mnemonic file");
 	}
-	if ((f2 = fopen(argv[2],"r")) == NULL) {
+	if ((f2 = fopen(argv[2],"rb")) == NULL) {
 		error("cannot open class file");
 	}
 	convert(f1,f2);
diff --git a/util/ego/share/show.c b/util/ego/share/show.c
index 7741f0cbf..f709a62b7 100644
--- a/util/ego/share/show.c
+++ b/util/ego/share/show.c
@@ -93,7 +93,7 @@ main(argc, argv)
 	if (argc != 3 || argv[1][0] != '-') {
 		error("usage: %s -[ldpbc] filename",argv[0]);
 	}
-	if ((f = fopen(argv[2], "r")) == NULL) {
+	if ((f = fopen(argv[2], "rb")) == NULL) {
 		error("cannot open %s", argv[2]);
 	}
 	switch(argv[1][1]) {
diff --git a/util/opt/main.c b/util/opt/main.c
index 7b75fb5c0..10b9da0a8 100644
--- a/util/opt/main.c
+++ b/util/opt/main.c
@@ -59,8 +59,8 @@ void fileinit(void)
 	}
 	else
 	{
+		sys_setbinarymode(stdout);
 		outfile = stdout;
-		freopen(NULL, "wb", stdout);
 		outshort(sp_magic);
 	}
 }
@@ -85,10 +85,12 @@ int main(int argc, char* argv[])
 		exit(EXIT_FAILURE);
 	}
 	if (argc)
+	{
 		if (freopen(*argv, "rb", stdin) == NULL)
 			error("Cannot open %s", *argv);
+	}
 	else
-		freopen(NULL, "rb", stdin);
+		sys_setbinarymode(stdin);
 
 	fileinit();
 #ifdef USEMALLOC