diff --git a/src/cmd/gc/export.c b/src/cmd/gc/export.c
index 427f649f2c2..aaa32a11b2a 100644
--- a/src/cmd/gc/export.c
+++ b/src/cmd/gc/export.c
@@ -78,7 +78,7 @@ dumpexportconst(Sym *s)
 	case CTINT:
 	case CTSINT:
 	case CTUINT:
-		Bprint(bout, "0x%llux\n", mpgetfix(n->val.u.xval));
+		Bprint(bout, "%B\n", n->val.u.xval);
 		break;
 	case CTBOOL:
 		Bprint(bout, "0x%llux\n", n->val.u.bval);
diff --git a/src/cmd/gc/go.h b/src/cmd/gc/go.h
index af50d48bd36..16efdc9cb94 100644
--- a/src/cmd/gc/go.h
+++ b/src/cmd/gc/go.h
@@ -487,6 +487,7 @@ void	mpatofix(Mpint *a, char *s);
 void	mpatoflt(Mpflt *a, char *s);
 void	mpmovefltfix(Mpint *a, Mpflt *b);
 void	mpmovefixflt(Mpflt *a, Mpint *b);
+int	Bconv(Fmt*);
 
 /*
  *	mparith2.c
diff --git a/src/cmd/gc/lex.c b/src/cmd/gc/lex.c
index a1859b6e91b..200960dff9a 100644
--- a/src/cmd/gc/lex.c
+++ b/src/cmd/gc/lex.c
@@ -52,6 +52,7 @@ mainlex(int argc, char *argv[])
 	fmtinstall('N', Nconv);		// node pointer
 	fmtinstall('Z', Zconv);		// escaped string
 	fmtinstall('L', Lconv);		// line number
+	fmtinstall('B', Bconv);		// big numbers
 	
 	lexinit();
 	lineno = 1;
diff --git a/src/cmd/gc/mparith1.c b/src/cmd/gc/mparith1.c
index 6c625f3fd9f..189e43af6fb 100644
--- a/src/cmd/gc/mparith1.c
+++ b/src/cmd/gc/mparith1.c
@@ -348,3 +348,32 @@ bad:
 	warn("set ovf in mpatov: %s", as);
 	mpmovecfix(a, 0);
 }
+
+int
+Bconv(Fmt *fp)
+{
+	char buf[500], *p;
+	Mpint *xval, q, r, ten;
+	int f;
+
+	xval = va_arg(fp->args, Mpint*);
+	mpmovefixfix(&q, xval);
+	f = 0;
+	if(mptestfix(&q) < 0) {
+		f = 1;
+		mpnegfix(&q);
+	}
+	mpmovecfix(&ten, 10);
+
+	p = &buf[sizeof(buf)];
+	*--p = 0;
+	for(;;) {
+		mpdivmodfixfix(&q, &r, &q, &ten);
+		*--p = mpgetfix(&r) + '0';
+		if(mptestfix(&q) <= 0)
+			break;
+	}
+	if(f)
+		*--p = '-';
+	return fmtstrcpy(fp, p);
+}
diff --git a/src/cmd/gc/subr.c b/src/cmd/gc/subr.c
index 1f9043a4427..11cb870f9a4 100644
--- a/src/cmd/gc/subr.c
+++ b/src/cmd/gc/subr.c
@@ -1053,13 +1053,9 @@ Nconv(Fmt *fp)
 			snprint(buf1, sizeof(buf1), "LITERAL-ctype=%d", n->val.ctype);
 			break;
 		case CTINT:
-			snprint(buf1, sizeof(buf1), "I%lld", mpgetfix(n->val.u.xval));
-			break;
 		case CTSINT:
-			snprint(buf1, sizeof(buf1), "S%lld", mpgetfix(n->val.u.xval));
-			break;
 		case CTUINT:
-			snprint(buf1, sizeof(buf1), "U%lld", mpgetfix(n->val.u.xval));
+			snprint(buf1, sizeof(buf1), "I%B", n->val.u.xval);
 			break;
 		case CTFLT:
 			snprint(buf1, sizeof(buf1), "F%g", mpgetflt(n->val.u.fval));