diff --git a/internal/wwfixture/types.ww b/internal/wwfixture/types.ww
index ba27a00d..08d4c239 100644
--- a/internal/wwfixture/types.ww
+++ b/internal/wwfixture/types.ww
@@ -1,13 +1,13 @@
 package wwfixture;
 
 def protocolversion: i32 = 1;
-def corpuscount: i32 = 1236;
+def corpuscount: i32 = 1237;
 def errorcount: i32 = 314;
 def compilecount: i32 = 12;
-def runcount: i32 = 144;
+def runcount: i32 = 145;
 def runexitcount: i32 = 766;
-def nativecount: i32 = 2472;
-def corpushash: str = "4c8f4a693d2d8193b15f4215610c1d070dc83493b1189af772ca09cad4a69db7";
+def nativecount: i32 = 2474;
+def corpushash: str = "7763f2eb34524f67355114f5bdfbf3f64415152a8ec64060fe32a322bdbe1b24";
 
 type directive = enum i32 {
 	ERROR = 0,
diff --git a/selfhost/cmd/wcc/check.ww b/selfhost/cmd/wcc/check.ww
index 8cb6957f..3ebb6726 100644
--- a/selfhost/cmd/wcc/check.ww
+++ b/selfhost/cmd/wcc/check.ww
@@ -3328,6 +3328,22 @@ fn exprtype(c: *checker, e: *syntax.node, hint: *syntax.node) *syntax.node = {
 	};
 	if (k == syntax.nkind.N_BIN) {
 		let tn: *syntax.node = binoptype(c, e);
+		// #59.9: checkisas pre-stamps an enum OR-fold (`(m.A|m.B) as
+		// u32`) TY_ENUM and folds the member N_DOTs to int literals;
+		// this post-order revisit re-derives from those now-untyped
+		// literals and clobbered the stamp, so cgtypeassert's #27b
+		// reinterpret gate missed and emitted a phantom tagged assert
+		// (unconditional exit 1). Keep an existing enum stamp; the
+		// returned tnode contract for callers is unchanged.
+		let pre599: *syntax.tinfo = e.type_: *syntax.tinfo;
+		if (pre599 != nil) {
+			let prech: *syntax.tinfo = tichase(pre599);
+			if (prech != nil) {
+				if (prech.kind == syntax.tykind.TY_ENUM) {
+					return tn;
+				};
+			};
+		};
 		e.type_ = tinfofornode(c, tn): *void;
 		return tn;
 	};
@@ -6353,6 +6369,15 @@ fn checkisas(c: *checker, n: *syntax.node) void = {
 		if (n.lhs.kind == syntax.nkind.N_TRYPROP || n.lhs.kind == syntax.nkind.N_TRYUNW) {
 			st = exprtype(c, n.lhs, nil);
 		};
+		// #59.9: an N_BIN operand (`(m.A | m.B) as u32`) was never
+		// typed, so the OR-fold reached cgen unstamped and
+		// cgtypeassert's enum-reinterpret gate (#27b) missed —
+		// lowering a plain enum value as a phantom tagged assert
+		// (unconditional exit 1). cstage types the lhs
+		// unconditionally (cmd/wcc/check.c:2220 cexpr(c, n->lhs)).
+		if (n.lhs.kind == syntax.nkind.N_BIN) {
+			st = exprtype(c, n.lhs, nil);
+		};
 	};
 	let u: *syntax.node = resolvealias(c, unwrapbang(st));
 	if (u == nil) { return; };
diff --git a/test/wcc/989_lib_byteid.c b/test/wcc/989_lib_byteid.c
index 12e7fe09..642f16ef 100644
--- a/test/wcc/989_lib_byteid.c
+++ b/test/wcc/989_lib_byteid.c
@@ -169,8 +169,13 @@ static const struct ent ents[] = {
 	/* #59.7 siphash graduated to M_ID above (#61 fix) */
 	{ .fixture = "lib/log/logtest.ww",
 	  .mode = M_DIVERGE, .cite = "#59.8" },
+	/* #59.9 graduated: the wwstage checker never typed an N_BIN operand
+	 * of `as`, so an enum OR-fold reached cgen unstamped and lowered as
+	 * a phantom tagged assert (unconditional exit 1). checkisas now
+	 * types the N_BIN lhs and the post-order restamp preserves the enum
+	 * stamp. Runtime pin: r599_enum_orfold_as. */
 	{ .fixture = "lib/os/stattest.ww",
-	  .mode = M_DIVERGE, .cite = "#59.9" },
+	  .mode = M_ID, .cite = "#59.9 graduated by the checkisas N_BIN stamp" },
 	/* #59.10 stoftest graduated to M_ID above (#62 fix) */
 	{ .fixture = "lib/ww/syntax/toktest.ww", .inc = "lib/ww",
 	  .mode = M_ID, .cite = "#59.11 graduated by #146 str==" },
diff --git a/test/wcc/data/r599_enum_orfold_as/case.ww b/test/wcc/data/r599_enum_orfold_as/case.ww
new file mode 100644
index 00000000..f795f275
--- /dev/null
+++ b/test/wcc/data/r599_enum_orfold_as/case.ww
@@ -0,0 +1,16 @@
+//ww:run
+// #59.9: an enum member OR-fold under `as`. The pre-fix wwstage
+// checker never typed the N_BIN operand, so cgtypeassert's enum
+// reinterpret gate missed and lowered a phantom tagged assert that
+// unconditionally exited 1.
+package main;
+
+type mask = enum u32 { A = 1, B = 2, C = 4 };
+
+fn main() i32 = {
+	let w: u32 = (mask.A | mask.B | mask.C) as u32;
+	if (w != 7u32) { return 1; };
+	let v: u32 = (mask.A | mask.C) as u32;
+	if (v != 5u32) { return 2; };
+	return 0;
+};