diff --git a/cmd/wcc/check.c b/cmd/wcc/check.c
index f25c93d4..60506564 100644
--- a/cmd/wcc/check.c
+++ b/cmd/wcc/check.c
@@ -3230,14 +3230,31 @@ check_file(Checker *c, Node *file)
 		for (Node *d = file->list; d; d = d->next) {
 			if (d->kind != N_FNDECL)
 				continue;
-			int istest = 0;
+			int ntestattr = 0;
 			for (Node *at = d->attr; at; at = at->next)
-				if (at->str && strcmp(at->str, "test") == 0) {
-					istest = 1;
-					break;
-				}
-			if (!istest)
+				if (at->str && strcmp(at->str, "test") == 0)
+					ntestattr++;
+			if (ntestattr == 0)
 				continue;
+			/* Attribute-shape rejects, fixed order, first failure
+			 * wins per fn; wording is byte-stable with the wwstage
+			 * twin (check.ww). A silently-dropped shape here ships
+			 * a test that never runs. */
+			if (ntestattr > 1) {
+				err(c, d->pos, "duplicate @test on fn '%s'",
+				    d->str);
+				continue;
+			}
+			if (d->export) {
+				err(c, d->pos, "@test fn '%s' cannot be exported",
+				    d->str);
+				continue;
+			}
+			if (d->body == NULL) {
+				err(c, d->pos, "@test fn '%s' needs a body",
+				    d->str);
+				continue;
+			}
 			/* `fn f() void` parses the explicit `void` into d->lhs
 			 * (parse.c:1329), so void-returning is lhs==NULL OR an
 			 * N_TNAME "void" — not lhs==NULL alone. */
diff --git a/selfhost/cmd/wcc/check.ww b/selfhost/cmd/wcc/check.ww
index d5c557a7..d800a86f 100644
--- a/selfhost/cmd/wcc/check.ww
+++ b/selfhost/cmd/wcc/check.ww
@@ -7134,16 +7134,38 @@ export fn checkfile(c: *checker, file: *syntax.node) void = {
 		let t: *syntax.node = file.list;
 		for (t != nil) {
 			if (t.kind == syntax.nkind.N_FNDECL) {
-				let istest: bool = false;
+				let ntestattr: i32 = 0;
 				let at: *syntax.node = t.attr;
 				for (at != nil) {
 					if (at.kind == syntax.nkind.N_ATTR
 					    && syntax.streq(at.str, "test")) {
-						istest = true;
+						ntestattr += 1;
 					};
 					at = at.next;
 				};
-				if (istest) {
+				// Attribute-shape rejects, fixed order, first
+				// failure wins per fn; wording byte-stable with
+				// the cstage twin (check.c). A silently-dropped
+				// shape here ships a test that never runs.
+				if (ntestattr > 1) {
+					cerr(t.file);
+					cerr(": error: duplicate @test on fn '");
+					cerr(t.str);
+					cerr("'\n");
+					c.errs += 1;
+				} else { if (ntestattr == 1 && t.exported != 0) {
+					cerr(t.file);
+					cerr(": error: @test fn '");
+					cerr(t.str);
+					cerr("' cannot be exported\n");
+					c.errs += 1;
+				} else { if (ntestattr == 1 && t.body == nil) {
+					cerr(t.file);
+					cerr(": error: @test fn '");
+					cerr(t.str);
+					cerr("' needs a body\n");
+					c.errs += 1;
+				} else { if (ntestattr == 1) {
 					// `fn f() void` parses the explicit void
 					// into t.lhs, so void-returning is lhs==nil
 					// OR an N_TNAME "void".
@@ -7172,7 +7194,7 @@ export fn checkfile(c: *checker, file: *syntax.node) void = {
 						rtail = row;
 						ntest += 1i32;
 					};
-				};
+				}; }; }; };
 			};
 			t = t.next;
 		};
diff --git a/test/package/package_test.ww b/test/package/package_test.ww
index 3722588c..7cd417da 100644
--- a/test/package/package_test.ww
+++ b/test/package/package_test.ww
@@ -443,6 +443,52 @@ fn packagepath(relative: str) str = {
 	clean(root);
 };
 
+// Invalid @test attribute shapes reject at build with stable text on
+// BOTH frontends (the -T synth checker owns them; the fixture corpus
+// cannot reach -T, so these rows live here). Fragments only — the
+// stages' error-line prefixes legitimately differ (file:line:col vs
+// file:).
+@test fn invalid_test_shapes_reject() void = {
+	let root: str = fresh();
+	let shapes: []str = [
+		"@test export fn t() void = { };",
+		"@test fn t() void;",
+		"@test fn t(x: i32) void = { };",
+		"@test fn t() i32 = { return 0; };",
+		"@test @test fn t() void = { };",
+	];
+	let frags: []str = [
+		"@test fn 't' cannot be exported",
+		"@test fn 't' needs a body",
+		"@test fn 't' must be fn() void",
+		"@test fn 't' must be fn() void",
+		"duplicate @test on fn 't'",
+	];
+	let digits: []str = ["0", "1", "2", "3", "4"];
+	let outc: commandout;
+	let outw: commandout;
+	let i: i32 = 0;
+	for (i < shapes.len) {
+		let dir: str = strings.concat(root, "/shape", digits[i]);
+		assert(os.mkdir(dir, 448i32) == 0);
+		let src: str = strings.concat(dir, "/bad_test.ww");
+		writefile(src, strings.concat("package main;\n",
+			shapes[i], "\n"));
+		let avc: []str = [driver("ww"), "test", src];
+		let avw: []str = [driver("ww_ww"), "test", src];
+		runcommand(root, strings.concat("shape-c", digits[i]), avc,
+			(30i64 * (time.second: i64)): time.duration, &outc);
+		runcommand(root, strings.concat("shape-ww", digits[i]), avw,
+			(30i64 * (time.second: i64)): time.duration, &outw);
+		expectexit(&outc, 1);
+		expectexit(&outw, 1);
+		assert(has(outc.stderr, frags[i]));
+		assert(has(outw.stderr, frags[i]));
+		i += 1;
+	};
+	clean(root);
+};
+
 // Go's ./... parity: a trailing "..." element walks the tree, one package
 // run per test-bearing directory, dot- and underscore-prefixed directory
 // names excluded. The excluded sentinels hold failing tests so a wrong