diff --git a/cmd/wcc/lex.c b/cmd/wcc/lex.c
index 440e9df3..886906bf 100644
--- a/cmd/wcc/lex.c
+++ b/cmd/wcc/lex.c
@@ -181,6 +181,9 @@ static u64
 parseint(const char *s, u64 n, int base, int *ok)
 {
 	u64 v = 0;
+	u64 b = (u64)base;
+	u64 cutoff = (u64)~0ULL / b;
+	u64 cutlim = (u64)~0ULL % b;
 	int got = 0;
 	for (u64 i = 0; i < n; i++) {
 		int c = (unsigned char)s[i];
@@ -192,9 +195,11 @@ parseint(const char *s, u64 n, int base, int *ok)
 		else if (c >= 'A' && c <= 'F') d = c - 'A' + 10;
 		else { *ok = 0; return 0; }
 		if (d >= base) { *ok = 0; return 0; }
-		/* overflow? cheap check */
-		if (v > (u64)~0ULL / (u64)base) { *ok = 0; return 0; }
-		v = v * (u64)base + (u64)d;
+		if (v > cutoff || (v == cutoff && (u64)d > cutlim)) {
+			*ok = 0;
+			return 0;
+		}
+		v = v * b + (u64)d;
 		got = 1;
 	}
 	*ok = got;
@@ -369,6 +374,7 @@ lexnum(Lex *l, Pos start)
 	/* A typed suffix must be glued (no whitespace) to the digits. */
 	if (isidstart(lpeek(l, 0))) {
 		u64 sb = l->pos;
+		i32 sc = l->col;
 		while (isidcont(lpeek(l, 0))) lget(l);
 		u64 sl = l->pos - sb;
 		const char *names[] = {
@@ -387,9 +393,8 @@ lexnum(Lex *l, Pos start)
 		if (match) {
 			t.tsuffix = astrndup(l->a, l->src + sb, sl);
 		} else {
-			/* not a known suffix — rewind so the run becomes a
-			 * separate token. */
 			l->pos = sb;
+			l->col = sc;
 		}
 	}
 	return t;
diff --git a/lib/ww/syntax/lex.ww b/lib/ww/syntax/lex.ww
index fa215d57..d9400657 100644
--- a/lib/ww/syntax/lex.ww
+++ b/lib/ww/syntax/lex.ww
@@ -269,6 +269,9 @@ fn skipws(l: *lex) bool = {
 
 fn parseint(p: *u8, n: u64, base: i32, ok: *bool) u64 = {
 	let v: u64 = 0u64;
+	let b: u64 = base: u64;
+	let cutoff: u64 = ~0u64 / b;
+	let cutlim: u64 = ~0u64 % b;
 	let got: bool = false;
 	let i: u64 = 0u64;
 	for (i < n) {
@@ -294,8 +297,11 @@ fn parseint(p: *u8, n: u64, base: i32, ok: *bool) u64 = {
 		};
 		if (d < 0) { *ok = false; return 0u64; };
 		if (d >= base) { *ok = false; return 0u64; };
-		if (v > ~0u64 / (base: u64)) { *ok = false; return 0u64; };
-		v = v * (base: u64) + (d: u64);
+		if (v > cutoff || (v == cutoff && (d: u64) > cutlim)) {
+			*ok = false;
+			return 0u64;
+		};
+		v = v * b + (d: u64);
 		got = true;
 		i += 1u64;
 	};
@@ -551,6 +557,7 @@ fn lexnum(l: *lex, start: *pos, out: *tok) void = {
 	if (pc >= 0) {
 		if (isidstart(pc: rune)) {
 			let sb: u64 = l.lpos;
+			let sc: i32 = l.col;
 			for (true) {
 				let cc: i32 = lpeek(l, 0u64);
 				if (cc < 0) { break; };
@@ -591,6 +598,7 @@ fn lexnum(l: *lex, start: *pos, out: *tok) void = {
 				out.tsuffix = strings.dup(view);
 			} else {
 				l.lpos = sb;
+				l.col = sc;
 			};
 		};
 	};
diff --git a/lib/ww/syntax/tok_test.ww b/lib/ww/syntax/tok_test.ww
index 69d00e66..442bdc98 100644
--- a/lib/ww/syntax/tok_test.ww
+++ b/lib/ww/syntax/tok_test.ww
@@ -309,3 +309,32 @@ fn checkfloat(src: str, want: u64) void = {
 	checkfloat("1.0e308", 0x7FE1CCF385EBC8A0u64);
 	checkfloat("2.225073858507202e-308", 0x0010000000000001u64);
 };
+
+@test fn intfinalband() void = {
+	let src: str = "18446744073709551616";
+	let l: lex;
+	lexinit(&l, "t", src.ptr, src.len: u64);
+	let t: tok;
+	lexnext(&l, &t);
+	assert(!(t.kind != tkind.TK_ERR));
+	assert(!(l.errs != 1));
+};
+
+@test fn suffixrewindcols() void = {
+	let src: str = "1foo bar";
+	let l: lex;
+	lexinit(&l, "t", src.ptr, src.len: u64);
+	let t: tok;
+	lexnext(&l, &t);
+	assert(!(t.kind != tkind.TK_INT));
+	assert(!(t.col != 1));
+	assert(!(t.uval != 1u64));
+	lexnext(&l, &t);
+	assert(!(t.kind != tkind.TK_IDENT));
+	assert(!(t.col != 2));
+	assert(!(t.text != "foo"));
+	lexnext(&l, &t);
+	assert(!(t.kind != tkind.TK_IDENT));
+	assert(!(t.col != 6));
+	assert(!(t.text != "bar"));
+};
diff --git a/test/wcc/100_lex.c b/test/wcc/100_lex.c
index 38d13dd7..e549d666 100644
--- a/test/wcc/100_lex.c
+++ b/test/wcc/100_lex.c
@@ -80,6 +80,7 @@ static const struct row rows[] = {
 	{ "0xDE_AD_BE_EF",   "INT(3735928559)" },
 	{ "0b1010",          "INT(10)" },
 	{ "0o777",           "INT(511)" },
+	{ "18446744073709551616", "ERR(18446744073709551616)" },
 	{ "3.14",            "FLOAT(3.14)" },
 	{ "1.5e3",           "FLOAT(1500)" },
 
@@ -149,6 +150,28 @@ runerr(const char *src)
 	return ok;
 }
 
+static int
+runrewind(void)
+{
+	const char *src = "1foo bar";
+	Arena *a = newarena();
+	Lex l;
+	lexinit(&l, a, "<test>", src, strlen(src));
+	Tok n = lexnext(&l);
+	Tok f = lexnext(&l);
+	Tok b = lexnext(&l);
+	int ok = n.kind == TK_INT && n.pos.col == 1 && n.v.uval == 1
+	    && f.kind == TK_IDENT && f.pos.col == 2
+	    && strcmp(f.text, "foo") == 0
+	    && b.kind == TK_IDENT && b.pos.col == 6
+	    && strcmp(b.text, "bar") == 0;
+	if (!ok)
+		fprintf(stderr, "suffix rewind columns: want 1,2,6 got %d,%d,%d\n",
+		    n.pos.col, f.pos.col, b.pos.col);
+	freearena(a);
+	return ok;
+}
+
 static const char *const errrows[] = {
 	"'\\uZ'",		/* unexpected rune scanning for escape */
 	"\"\\u00g0\"",		/* non-hex digit inside a string escape */
@@ -169,6 +192,8 @@ main(void)
 			fail++;
 		}
 	}
+	if (!runrewind())
+		fail++;
 	for (size_t i = 0; i < sizeof errrows / sizeof errrows[0]; i++) {
 		if (!runerr(errrows[i])) {
 			fprintf(stderr, "errrow %zu failed\n", i);
diff --git a/test/wcc/data/r989_intoverflow_dec_overflow/case.ww b/test/wcc/data/r989_intoverflow_dec_overflow/case.ww
index 3ce1e089..b61f43d5 100644
--- a/test/wcc/data/r989_intoverflow_dec_overflow/case.ww
+++ b/test/wcc/data/r989_intoverflow_dec_overflow/case.ww
@@ -1,7 +1,7 @@
 //ww:error "bad integer literal"
-// 989_intoverflow_reject dec_overflow: a 21-digit decimal exceeds u64.
+// Exact final-digit band: MAX/10 with 6 greater than MAX%10.
 package main;
 export fn main() i32 = {
-	let x: u64 = 99999999999999999999u64;
+	let x: u64 = 18446744073709551616u64;
 	return x: i32;
 };