diff --git a/mach/proto/as/comm7.c b/mach/proto/as/comm7.c
index 3c7871fbe..e95037305 100644
--- a/mach/proto/as/comm7.c
+++ b/mach/proto/as/comm7.c
@@ -363,7 +363,8 @@ char *path, *tail;
 	if ((dir = getenv("TMPDIR")) == NULL)
 		dir = tmp_dir;
 	sprintf(path, "%s/%s", dir, tail);
-	return(ffcreat(mktemp(path)));
+	close(mkstemp(path));
+	return(ffcreat(path));
 }
 
 /* ---------- Error handling ---------- */
diff --git a/modules/src/em_code/insert.c b/modules/src/em_code/insert.c
index fd88cd4ec..36950c3ea 100644
--- a/modules/src/em_code/insert.c
+++ b/modules/src/em_code/insert.c
@@ -145,7 +145,8 @@ swttmp()
 
 		strcpy(p, C_tmpdir);
 		strcat(p, "/CodeXXXXXX");
-		C_tmpfile = mktemp(p);
+		close(mkstemp(p));
+		C_tmpfile = p;
 		if (! sys_open(p, OP_WRITE, &C_old_ofp)) {
 			C_failed();
 		}
@@ -250,7 +251,7 @@ mkpart(part)
 	*/
 	register Part *p = C_findpart(part);
 	register int index = part % TABSIZ;
-	
+
 	if (p != 0) {
 		/* multiple defined part ... */
 		C_internal_error();
diff --git a/modules/src/system/lock.c b/modules/src/system/lock.c
index 0f6be5985..6f00a3a16 100644
--- a/modules/src/system/lock.c
+++ b/modules/src/system/lock.c
@@ -4,6 +4,8 @@
  */
 /* $Id$ */
 
+#include <string.h>
+#include <stdlib.h>
 #include "system.h"
 
 int
@@ -12,7 +14,6 @@ sys_lock(path)
 {
 	char buf[1024];
 	char *tmpf = ".lockXXXXXX";
-	char *strrchr(), *strcpy(), *mktemp();
 	char *p;
 	int ok, fd;
 
@@ -23,8 +24,7 @@ sys_lock(path)
 	}
 	else
 		strcpy(buf, tmpf);
-	mktemp(buf);
-	if ((fd = creat(buf, 0)) < 0)
+	if ((fd = mkstemp(buf)) < 0)
 		return 0;
 	close(fd);
 	ok = (link(buf, path) == 0);
diff --git a/util/LLgen/src/main.c b/util/LLgen/src/main.c
index ca4b05f22..1bd31aa46 100644
--- a/util/LLgen/src/main.c
+++ b/util/LLgen/src/main.c
@@ -37,7 +37,6 @@ extern		fatal();
 extern		comfatal();
 extern		copyfile();
 extern void install();
-extern char	*mktemp();
 extern char	*sbrk();
 
 main(argc,argv) register string	argv[]; {
@@ -164,8 +163,8 @@ main(argc,argv) register string	argv[]; {
 	    nc_rec_file = libpath ("nc_rec");
 	}
 #endif
-	mktemp(f_temp);
-	mktemp(f_pars);
+	close(mkstemp(f_temp));
+	close(mkstemp(f_pars));
 	if ((fact = fopen(f_temp,"w")) == NULL) {
 		fputs("Cannot create temporary\n",stderr);
 		exit(1);
diff --git a/util/amisc/astrip.c b/util/amisc/astrip.c
index e96617abf..e82cb27f1 100644
--- a/util/amisc/astrip.c
+++ b/util/amisc/astrip.c
@@ -17,8 +17,6 @@
 
 char	temp_name[] = "/tmp/sXXXXXX";
 char	*tname;
-char	*mktemp();
-FILE	*fopen();
 FILE	*tf;
 struct outhead buf;
 int	readerror, writeerror;
@@ -31,12 +29,12 @@ char **argv;
 	signal(SIGHUP, SIG_IGN);
 	signal(SIGINT, SIG_IGN);
 	signal(SIGQUIT, SIG_IGN);
-	tname = mktemp(temp_name);
+	close(mkstemp(temp_name));
 	while(--argc) {
 		if ((status = strip(argv[argc])) > 1)
 			break;
 	}
-	unlink(tname);
+	unlink(temp_name);
 	exit(status);
 }
 
diff --git a/util/arch/archiver.c b/util/arch/archiver.c
index 65684232a..2be5fd3ad 100644
--- a/util/arch/archiver.c
+++ b/util/arch/archiver.c
@@ -106,7 +106,6 @@ char *progname;
 
 char temp_buf[32];
 char *temp_arch = &temp_buf[0];
-extern char *mktemp();
 extern char *ctime();
 
 void do_object(int f, long size);
@@ -277,7 +276,7 @@ char *argv[];
 	|| app_fl
 #endif
      ) {
-	mktemp(temp_arch);
+	close(mkstemp(temp_arch));
   }
 #ifdef AAL
   tab = (struct ranlib *) malloc(512 * sizeof(struct ranlib));
diff --git a/util/byacc/main.c b/util/byacc/main.c
index 32982239c..b7f5e8f0c 100644
--- a/util/byacc/main.c
+++ b/util/byacc/main.c
@@ -1,3 +1,4 @@
+#include <stdlib.h>
 #include <signal.h>
 #include "defs.h"
 
@@ -56,10 +57,6 @@ char  *rassoc;
 short **derives;
 char *nullable;
 
-extern char *mktemp();
-extern char *getenv();
-
-
 done(k)
 int k;
 {
@@ -253,9 +250,9 @@ create_file_names()
     text_file_name[len + 5] = 't';
     union_file_name[len + 5] = 'u';
 
-    mktemp(action_file_name);
-    mktemp(text_file_name);
-    mktemp(union_file_name);
+    close(mkstemp(action_file_name));
+    close(mkstemp(text_file_name));
+    close(mkstemp(union_file_name));
 
     len = strlen(file_prefix);
 
diff --git a/util/ego/em_ego/em_ego.c b/util/ego/em_ego/em_ego.c
index d29be7385..543f0b50b 100644
--- a/util/ego/em_ego/em_ego.c
+++ b/util/ego/em_ego/em_ego.c
@@ -280,7 +280,7 @@ static void
 				phargs[argc++] = "-M";
 				phargs[argc++] = descr_file;
 			}
-			
+
 			for (i=0; i<nphase_args; i++)
 				phargs[argc++] = phase_args[i];
 
@@ -410,12 +410,12 @@ int main(int argc, char* argv[])
 		(void)strcpy(tmpbufs[0], ".");
 	}
 	(void)strcat(ddump, "/ego.dd.XXXXXX");
-	(void)mktemp(ddump);
+	close(mkstemp(ddump));
 	(void)strcat(pdump, "/ego.pd.XXXXXX");
-	(void)mktemp(pdump);
+	close(mkstemp(pdump));
 
 	(void)strcat(tmpbufs[0], "/ego.XXXXXX");
-	(void)mktemp(tmpbufs[0]);
+	close(mkstemp(tmpbufs[0]));
 	(void)strcat(tmpbufs[0], ".A.BB");
 	for (i = 2 * NTEMPS - 1; i >= 1; i--)
 	{
diff --git a/util/ego/il/il.c b/util/ego/il/il.c
index 938dfa3cc..8313cb93e 100644
--- a/util/ego/il/il.c
+++ b/util/ego/il/il.c
@@ -334,10 +334,10 @@ char* argv[];
 	strcat(ccname, "/ego.i2.XXXXXX");
 	strcat(sname, "/ego.i3.XXXXXX");
 	strcat(cname2, "/ego.i4.XXXXXX");
-	mktemp(cname);
-	mktemp(ccname);
-	mktemp(sname);
-	mktemp(cname2);
+	close(mkstemp(cname));
+	close(mkstemp(ccname));
+	close(mkstemp(sname));
+	close(mkstemp(cname2));
 	pass1(files->lname_in, files->bname_in, cname); /* grep calls, analyse procedures */
 	space = total_size * space / 100;
 	pass2(cname, space); /* select calls to be expanded */
diff --git a/util/flex/main.c b/util/flex/main.c
index fad1a3fa8..d6f0ec936 100644
--- a/util/flex/main.c
+++ b/util/flex/main.c
@@ -6,7 +6,7 @@
  *
  * This code is derived from software contributed to Berkeley by
  * Vern Paxson.
- * 
+ *
  * The United States Government has rights in this work pursuant
  * to contract no. DE-AC03-76SF00098 between the United States
  * Department of Energy and the University of California.
@@ -38,6 +38,7 @@ static char rcsid[] =
 #endif
 
 
+#include <stdlib.h>
 #include "flexdef.h"
 
 static char flex_version[] = "2.3";
@@ -394,7 +395,7 @@ char **argv;
 
     {
     int i, sawcmpflag;
-    char *arg, *flex_gettime(), *mktemp();
+    char *arg, *flex_gettime();
 
     printstats = syntaxerror = trace = spprdflt = interactive = caseins = false;
     backtrack_report = performance_report = ddebug = fulltbl = fullspd = false;
@@ -611,7 +612,7 @@ get_next_arg: /* used by -C and -S flags in lieu of a "continue 2" control */
 #else
 	(void) strcpy( temp_action_file_name, "flexXXXXXX.tmp" );
 #endif
-	(void) mktemp( temp_action_file_name );
+	close(mkstemp(temp_action_file_name));
 
 	action_file_name = temp_action_file_name;
 	}
diff --git a/util/opt/main.c b/util/opt/main.c
index 2990b22b2..a3df98a73 100644
--- a/util/opt/main.c
+++ b/util/opt/main.c
@@ -57,13 +57,12 @@ flags(s) register char *s; {
 }
 
 fileinit() {
-	char *mktemp();
 	short readshort();
 
 	if (readshort() != (short) sp_magic)
 		error("wrong input file");
 	if (Lflag) {
-		outfile = fopen(mktemp(template),"w");
+		outfile = fdopen(mkstemp(template),"w");
 		if (outfile == NULL)
 			error("can't create %s",template);
 	} else {