diff --git a/exec.c b/exec.c
index c5120e8..75dceb7 100644
--- a/exec.c
+++ b/exec.c
@@ -2,7 +2,7 @@
 
 #include "sh.h"
 
-__RCSID("$MirOS: src/bin/mksh/exec.c,v 1.35 2007/07/22 13:38:26 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/exec.c,v 1.36 2007/07/22 14:01:48 tg Exp $");
 
 static int comexec(struct op *, struct tbl *volatile, const char **,
     int volatile);
@@ -95,7 +95,7 @@ execute(struct op *volatile t,
 				 */
 				if (tp && tp->type == CSHELL &&
 				    (tp->flag & SPEC_BI))
-					errorf("");
+					errorfz();
 				/* Deal with FERREXIT, quitenv(), etc. */
 				goto Break;
 			}
diff --git a/expr.c b/expr.c
index df75f90..79f4980 100644
--- a/expr.c
+++ b/expr.c
@@ -2,7 +2,7 @@
 
 #include "sh.h"
 
-__RCSID("$MirOS: src/bin/mksh/expr.c,v 1.11 2007/07/22 13:34:49 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/expr.c,v 1.12 2007/07/22 14:01:48 tg Exp $");
 
 /* The order of these enums is constrained by the order of opinfo[] */
 enum token {
@@ -178,7 +178,7 @@ v_evaluate(struct tbl *vp, const char *expr, volatile int error_ok,
 		if (i == LAEXPR) {
 			if (error_ok == KSH_RETURN_ERROR)
 				return (0);
-			errorf("");
+			errorfz();
 		}
 		unwind(i);
 		/* NOTREACHED */
diff --git a/funcs.c b/funcs.c
index 222493a..7fa786d 100644
--- a/funcs.c
+++ b/funcs.c
@@ -5,7 +5,7 @@
 
 #include "sh.h"
 
-__RCSID("$MirOS: src/bin/mksh/funcs.c,v 1.59 2007/07/22 13:34:49 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/funcs.c,v 1.60 2007/07/22 14:01:48 tg Exp $");
 
 int
 c_cd(const char **wp)
@@ -1142,7 +1142,7 @@ c_kill(const char **wp)
 		    "Usage: kill [ -s signame | -signum | -signame ] {pid|job}...\n"
 		    "       kill -l [exit_status]\n");
 #endif
-		bi_errorf("");
+		bi_errorfz();
 		return 1;
 	}
 
diff --git a/histrap.c b/histrap.c
index c1e3901..0062292 100644
--- a/histrap.c
+++ b/histrap.c
@@ -3,7 +3,7 @@
 
 #include "sh.h"
 
-__RCSID("$MirOS: src/bin/mksh/histrap.c,v 1.52 2007/07/22 13:34:50 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/histrap.c,v 1.53 2007/07/22 14:01:49 tg Exp $");
 
 Trap sigtraps[NSIG + 1];
 static struct sigaction Sigact_ign;
@@ -173,7 +173,6 @@ c_fc(const char **wp)
 	/* List history */
 	if (lflag) {
 		char *s, *t;
-		const char *nfmt = nflag ? "\t" : "%d\t";
 
 		for (hp = rflag ? hlast : hfirst;
 		    hp >= hfirst && hp <= hlast; hp += rflag ? -1 : 1) {
diff --git a/lex.c b/lex.c
index e083b9e..fd3f43d 100644
--- a/lex.c
+++ b/lex.c
@@ -2,7 +2,7 @@
 
 #include "sh.h"
 
-__RCSID("$MirOS: src/bin/mksh/lex.c,v 1.44 2007/07/22 13:34:51 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/lex.c,v 1.45 2007/07/22 14:01:49 tg Exp $");
 
 /* Structure to keep track of the lexing state and the various pieces of info
  * needed for each particular state. */
@@ -905,7 +905,7 @@ yyerror(const char *fmt, ...)
 	va_start(va, fmt);
 	shf_vfprintf(shl_out, fmt, va);
 	va_end(va);
-	errorf("");
+	errorfz();
 }
 
 /*
diff --git a/misc.c b/misc.c
index e96db67..fa60198 100644
--- a/misc.c
+++ b/misc.c
@@ -6,7 +6,7 @@
 #include <grp.h>
 #endif
 
-__RCSID("$MirOS: src/bin/mksh/misc.c,v 1.62 2007/07/22 13:38:26 tg Exp $\t"
+__RCSID("$MirOS: src/bin/mksh/misc.c,v 1.63 2007/07/22 14:01:49 tg Exp $\t"
 	MKSH_SH_H_ID);
 
 #undef USE_CHVT
@@ -853,7 +853,7 @@ ksh_getopt(const char **argv, Getopt *go, const char *optionsp)
 			    (go->flags & GF_NONAME) ? "" : argv[0],
 			    (go->flags & GF_NONAME) ? "" : ": ", c);
 			if (go->flags & GF_ERROR)
-				bi_errorf("");
+				bi_errorfz();
 		}
 		return '?';
 	}
@@ -879,7 +879,7 @@ ksh_getopt(const char **argv, Getopt *go, const char *optionsp)
 			    (go->flags & GF_NONAME) ? "" : argv[0],
 			    (go->flags & GF_NONAME) ? "" : ": ", c);
 			if (go->flags & GF_ERROR)
-				bi_errorf("");
+				bi_errorfz();
 			return '?';
 		}
 		go->p = 0;
diff --git a/sh.h b/sh.h
index 0669114..6fa72ad 100644
--- a/sh.h
+++ b/sh.h
@@ -8,7 +8,7 @@
 /*	$OpenBSD: c_test.h,v 1.4 2004/12/20 11:34:26 otto Exp $	*/
 /*	$OpenBSD: tty.h,v 1.5 2004/12/20 11:34:26 otto Exp $	*/
 
-#define MKSH_SH_H_ID "$MirOS: src/bin/mksh/sh.h,v 1.160 2007/07/22 13:46:15 tg Exp $"
+#define MKSH_SH_H_ID "$MirOS: src/bin/mksh/sh.h,v 1.161 2007/07/22 14:01:50 tg Exp $"
 #define MKSH_VERSION "R30 2007/07/22"
 
 #if HAVE_SYS_PARAM_H
@@ -1338,6 +1338,18 @@ void warningf(bool, const char *, ...)
     __attribute__((format (printf, 2, 3)));
 void bi_errorf(const char *, ...)
     __attribute__((format (printf, 1, 2)));
+/*
+ * circumvent compiler format string nonnull checking
+ * we teach xlC to not bitch about zero-lengths, want
+ * gcc to do it, and so gain double-checking benefits
+ */
+#if defined(__xlC__)
+#define errorfz()	errorf("")
+#define bi_errorfz()	bi_errorf("")
+#else
+#define errorfz()	errorf(null)
+#define bi_errorfz()	bi_errorf(null)
+#endif
 void internal_errorf(const char *, ...)
     __attribute__((noreturn))
     __attribute__((format (printf, 1, 2)));
diff --git a/var.c b/var.c
index 01d3b52..4fa3c09 100644
--- a/var.c
+++ b/var.c
@@ -2,7 +2,7 @@
 
 #include "sh.h"
 
-__RCSID("$MirOS: src/bin/mksh/var.c,v 1.41 2007/07/22 13:34:52 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/var.c,v 1.42 2007/07/22 14:01:50 tg Exp $");
 
 /*
  * Variables
@@ -341,7 +341,7 @@ setstr(struct tbl *vq, const char *s, int error_ok)
 	if ((vq->flag & RDONLY) && !no_ro_check) {
 		warningf(true, "%s: is read only", vq->name);
 		if (!error_ok)
-			errorf("");
+			errorfz();
 		return 0;
 	}
 	if (!(vq->flag&INTEGER)) { /* string dest */
@@ -690,7 +690,7 @@ typeset(const char *var, Tflag set, Tflag clr, int field, int base)
 			}
 		}
 		if (!ok)
-			errorf("");
+			errorfz();
 	}
 
 	if (val != NULL) {