diff --git a/Makefile b/Makefile
index 01f7b832..bba66f4f 100644
--- a/Makefile
+++ b/Makefile
@@ -248,6 +248,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_voidless_return_reject \
 	  $(BIN)/test_const_reassign_reject \
 	  $(BIN)/test_dupfield_reject \
+	  $(BIN)/test_enum_reject \
 	  $(BIN)/test_size_untyped_int \
 	  $(BIN)/test_tagged_staticinit \
 	  $(BIN)/test_arr_infer_len \
@@ -1549,6 +1550,12 @@ $(BIN)/test_dupfield_reject: test/wcc/849_dupfield_reject.c $(BIN)/ww \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_enum_reject: test/wcc/850_enum_reject.c $(BIN)/ww \
+		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
+		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_tagged_staticinit: test/wcc/843_tagged_staticinit.c $(BIN)/ww \
 		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
diff --git a/selfhost/cmd/wcc/check.ww b/selfhost/cmd/wcc/check.ww
index e022e30e..6f0547d3 100644
--- a/selfhost/cmd/wcc/check.ww
+++ b/selfhost/cmd/wcc/check.ww
@@ -788,7 +788,7 @@ fn resolvewalk(c: *checker, n: *syntax.node) void = {
 		};
 	};
 
-	if (k == syntax.nkind.N_TENUM) { stampenumvals(c, n); };
+	if (k == syntax.nkind.N_TENUM) { stampenumvals(c, n); validateenummembers(c, n); };
 	if (k == syntax.nkind.N_TSTRUCT) { validatestructfields(c, n); };
 
 	// #42's size/align/offset fold trigger lived here pre-A.6.0; the
@@ -1894,6 +1894,72 @@ fn validatestructfields(c: *checker, n: *syntax.node) void = {
 	};
 };
 
+// validateenummembers — reject the three invalid enum-decl shapes
+// cstage rejects at cmd/wcc/check.c:1000-1042 (the N_TENUM arm of
+// resolve_type): a non-integer storage type, a duplicate member name,
+// and an unfoldable (non-constant) member value-expr. Pure diagnostic:
+// it mutates no n.type_ / member value / checker state beyond bumping
+// c.errs, so valid programs (integer storage, distinct members,
+// foldable values) emit nothing and their stamping/codegen is untouched
+// — the byte-id safety condition. Fires once per enum decl from
+// resolvewalk's eager type-decl dispatch, sibling to validatestructfields
+// (rule-10 symmetric with cstage's once-per-resolve_type), not from the
+// per-query size/align arms.
+fn validateenummembers(c: *checker, n: *syntax.node) void = {
+	// storage type: cstage resolves n->lhs then gates type_isint
+	// (check.c:1004-1009); default storage is i32, always integer.
+	if (n.lhs != nil) {
+		let s: *syntax.tinfo = tinfofornode(c, n.lhs);
+		if (!syntax.typeisint(s)) {
+			cerr(n.lhs.file);
+			cerr(": error: enum storage type must be integer\n");
+			c.errs += 1;
+		};
+	};
+	let m: *syntax.node = n.list;
+	for (m != nil) {
+		if (m.kind == syntax.nkind.N_TENUMMEMBER && m.str.len != 0) {
+			// duplicate member: cstage compares each member against
+			// the earlier ones (check.c:1024-1032).
+			let e: *syntax.node = n.list;
+			for (e != m) {
+				if (e.kind == syntax.nkind.N_TENUMMEMBER
+				    && e.str.len != 0
+				    && syntax.streq(e.str, m.str)) {
+					cerr(m.file);
+					cerr(": error: duplicate enum member '");
+					cerr(m.str);
+					cerr("'\n");
+					c.errs += 1;
+					break;
+				};
+				e = e.next;
+			};
+		};
+		// unfoldable value: cstage delegates to eval_enum_value
+		// (check.c:1020), which emits a SHAPE-SPECIFIC reason —
+		// "enum value: unknown identifier 'B'" for a forward sibling
+		// ref (check.c:316), "...division by zero" (327), "...unsupported
+		// binary/unary op" (330/343), else the generic constant-expr
+		// message (349). enumvalfold returns a bare bool (no reason), so
+		// wwstage collapses all of these to the generic "enum value must
+		// be a constant integer expression". Both stages REJECT (errs
+		// counted, build gated) → functionally symmetric, no asm impact;
+		// the message-specificity gap is the lone divergence, retained
+		// and tracked as task #10 (rule-7: documented, not silent).
+		// `until = m` enforces harec's forward-only sibling-ref discipline.
+		if (m.lhs != nil) {
+			let v: u64 = 0u64;
+			if (!enumvalfold(n, m, m.lhs, &v)) {
+				cerr(m.file);
+				cerr(": error: enum value must be a constant integer expression\n");
+				c.errs += 1;
+			};
+		};
+		m = m.next;
+	};
+};
+
 // stampnilexpr — stamp nil-typed nodes in a constant expr subtree to
 // `ti`. lhs/rhs cover the enum constexpr grammar enumvalfold accepts
 // (literals, unary, binary, sibling backref); non-nil nodes keep the
diff --git a/test/wcc/850_enum_reject.c b/test/wcc/850_enum_reject.c
new file mode 100644
index 00000000..2b51d99b
--- /dev/null
+++ b/test/wcc/850_enum_reject.c
@@ -0,0 +1,189 @@
+/*
+ * 850_enum_reject (catB-2) — cstage and wwstage LOUD-REJECT the three
+ * invalid enum-declaration shapes: a non-integer storage type, a
+ * duplicate member name, and an unfoldable (non-constant) member value.
+ *
+ * cstage already rejected at cmd/wcc/check.c:1000-1042 (the N_TENUM arm
+ * of resolve_type — storage type_isint gate, the per-member dup walk,
+ * and eval_enum_value's constant fold). wwstage silently ACCEPTED — it
+ * stamped member types but never validated storage/dup/foldability. The
+ * fix adds validateenummembers(), a pure read-only diagnostic fired once
+ * per enum decl from resolvewalk's eager type-decl dispatch (selfhost/
+ * cmd/wcc/check.ww), the rule-10 twin of cstage's once-per-resolve_type
+ * site, sibling to validatestructfields (catB-7/14).
+ *
+ * Byte-id: pure diagnostic, no n.type_ / member-value / checker-state
+ * mutation; the valid corpus has integer storage, distinct members, and
+ * foldable values, so codegen of every valid program is unchanged →
+ * cstage == wwstage byte-id holds.
+ *
+ *   row          | shape                                | expect
+ *   -------------+--------------------------------------+--------
+ *   nonint_stor  | enum f64 { A }                       | REJECT
+ *   dup_member   | enum { A, B, A }                     | REJECT
+ *   fwd_ref      | enum { A = B, B }   (non-constant)   | REJECT
+ *   distinct     | enum { A, B=5, C=B+1 }, use A+C      | BUILD, run 6
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+static int
+runwait(const char *cmd)
+{
+	int rc = system(cmd);
+	if (rc == -1) return -1;
+	if (WIFEXITED(rc)) return WEXITSTATUS(rc);
+	return -1;
+}
+
+static void
+outbin(char *dst, size_t n, const char *tmpdir, const char *src)
+{
+	const char *base = strrchr(src, '/');
+	base = base ? base + 1 : src;
+	snprintf(dst, n, "%s/%s", tmpdir, base);
+	char *dot = strrchr(dst, '.');
+	if (dot && strcmp(dot, ".ww") == 0) *dot = '\0';
+}
+
+static int
+build_should_fail(const char *driver, const char *label, const char *src,
+    int i)
+{
+	char s[64], tmpdir[64], cmd[1024], bin[128];
+	snprintf(s, sizeof s, "/tmp/enr_%d_%d.ww", getpid(), i);
+	snprintf(tmpdir, sizeof tmpdir, "/tmp/enr_%d_d_%d", getpid(), i);
+	FILE *f = fopen(s, "wb");
+	if (!f) return -1;
+	fputs(src, f);
+	fclose(f);
+	mkdir(tmpdir, 0755);
+	snprintf(cmd, sizeof cmd, "cd %s && %s build %s 2>/dev/null",
+	    tmpdir, driver, s);
+	int rc = runwait(cmd);
+	outbin(bin, sizeof bin, tmpdir, s);
+	unlink(s);
+	unlink(bin);
+	rmdir(tmpdir);
+	if (rc == 0)
+		fprintf(stderr, "enr[%s][%s]: built ok, expected a reject\n",
+		    driver, label);
+	return rc == 0 ? -1 : 0;
+}
+
+static int
+run_build(const char *driver, const char *label, const char *src, int i)
+{
+	char s[64], tmpdir[64], cmd[1024], bin[128];
+	snprintf(s, sizeof s, "/tmp/enr_ok_%d_%d.ww", getpid(), i);
+	snprintf(tmpdir, sizeof tmpdir, "/tmp/enr_ok_%d_d_%d", getpid(), i);
+	FILE *f = fopen(s, "wb");
+	if (!f) return -1;
+	fputs(src, f);
+	fclose(f);
+	mkdir(tmpdir, 0755);
+	snprintf(cmd, sizeof cmd, "cd %s && %s build %s 2>/dev/null",
+	    tmpdir, driver, s);
+	if (runwait(cmd) != 0) {
+		fprintf(stderr, "enr[%s][%s]: build failed (valid enum must "
+		    "compile)\n", driver, label);
+		unlink(s); rmdir(tmpdir);
+		return -1;
+	}
+	outbin(bin, sizeof bin, tmpdir, s);
+	int got = runwait(bin);
+	unlink(s); unlink(bin); rmdir(tmpdir);
+	return got;
+}
+
+struct rejrow { const char *label; const char *src; };
+
+static const struct rejrow reject_rows[] = {
+	{ "nonint_stor",
+	  "package main;\n"
+	  "type e = enum f64 { A };\n"
+	  "fn main() i32 = { return e.A as i32; };\n" },
+	{ "dup_member",
+	  "package main;\n"
+	  "type e = enum { A, B, A };\n"
+	  "fn main() i32 = { return e.A as i32; };\n" },
+	{ "fwd_ref",
+	  "package main;\n"
+	  "type e = enum { A = B, B };\n"
+	  "fn main() i32 = { return e.A as i32; };\n" },
+};
+
+struct okrow { const char *label; const char *src; int want; };
+
+static const struct okrow ok_rows[] = {
+	{ "distinct",
+	  "package main;\n"
+	  "type e = enum { A, B = 5, C = B + 1 };\n"
+	  "fn main() i32 = { return e.A as i32 + e.C as i32; };\n",
+	  6 },
+};
+
+int
+main(void)
+{
+	const char *bin = getenv("BIN");
+	if (!bin) bin = "out/bin";
+	char absbin[1024];
+	if (bin[0] != '/') {
+		char cwd[1024];
+		if (getcwd(cwd, sizeof cwd) == NULL) return 1;
+		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
+		bin = absbin;
+	}
+
+	char cdrv[1024], wdrv[1024];
+	snprintf(cdrv, sizeof cdrv, "%s/ww", bin);
+	snprintf(wdrv, sizeof wdrv, "%s/ww_ww", bin);
+
+	struct { const char *name; const char *path; int gated; } drivers[] = {
+		{ "cstage",  cdrv, 0 },
+		{ "wwstage", wdrv, 1 },
+		{ NULL, NULL, 0 },
+	};
+
+	int nrej = (int)(sizeof reject_rows / sizeof reject_rows[0]);
+	int nok = (int)(sizeof ok_rows / sizeof ok_rows[0]);
+	int total = 0, fail = 0;
+
+	for (int d = 0; drivers[d].name; d++) {
+		if (drivers[d].gated && access(drivers[d].path, X_OK) != 0) {
+			fprintf(stderr, "enr: skip %s (no %s)\n",
+			    drivers[d].name, drivers[d].path);
+			continue;
+		}
+		for (int i = 0; i < nrej; i++) {
+			total++;
+			if (build_should_fail(drivers[d].path,
+			    reject_rows[i].label, reject_rows[i].src,
+			    d * 100 + i) != 0)
+				fail++;
+		}
+		for (int i = 0; i < nok; i++) {
+			total++;
+			int got = run_build(drivers[d].path, ok_rows[i].label,
+			    ok_rows[i].src, d * 100 + i);
+			if (got != ok_rows[i].want) {
+				fprintf(stderr, "enr[%s][%s]: exit=%d want=%d\n",
+				    drivers[d].name, ok_rows[i].label,
+				    got, ok_rows[i].want);
+				fail++;
+			}
+		}
+	}
+
+	if (fail) {
+		fprintf(stderr, "enr: %d/%d fixtures failed\n", fail, total);
+		return 1;
+	}
+	printf("enr: %d/%d ok\n", total, total);
+	return 0;
+}