diff --git a/assets/schema/cql-test-results.schema.json b/assets/schema/cql-test-results.schema.json
index 8f8e0cd..e8943f0 100644
--- a/assets/schema/cql-test-results.schema.json
+++ b/assets/schema/cql-test-results.schema.json
@@ -71,7 +71,8 @@
           },
           "invalid": {
             "type": "string",
-            "enum": ["true", "false", "semantic"]
+            "description": "The test's expected outcome, per InvalidType in testSchema.xsd: false to evaluate successfully, or the kind of error expected.",
+            "enum": ["false", "syntax", "semantic", "execution", "true"]
           },
           "capabilities": {
             "type": "array",
diff --git a/src/commands/build-cql-command.ts b/src/commands/build-cql-command.ts
index 57fbea4..c54eac0 100644
--- a/src/commands/build-cql-command.ts
+++ b/src/commands/build-cql-command.ts
@@ -4,6 +4,7 @@ import * as path from 'node:path';
 import { ConfigLoader } from '../conf/config-loader.js';
 import { TestLoader } from '../loaders/test-loader.js';
 import { generateEmptyResults } from '../shared/results-shared.js';
+import { preventsTranslation } from '../shared/invalid-utils.js';
 
 export class BuildCommand {
 	async execute(options: any): Promise<void> {
@@ -50,7 +51,9 @@ export class BuildCommand {
 				continue;
 			}
 
-			if (r.invalid !== 'semantic') {
+			// A define that cannot be translated would fail the whole generated library, so
+			// expressions expected to produce a syntax or semantic error are left out.
+			if (!preventsTranslation(r.invalid)) {
 				const defineVal = `define "${r.groupName}.${r.testName}": ${r.expression}`;
 				const key = `${r.testsName}-${r.groupName}-${r.testName}`;
 				let reason = '';
diff --git a/src/models/test-types.ts b/src/models/test-types.ts
index 7fc06ed..36e71f3 100644
--- a/src/models/test-types.ts
+++ b/src/models/test-types.ts
@@ -1,11 +1,13 @@
+import type { InvalidKind, ResultInvalidKind } from '../shared/invalid-utils.js';
+
 export interface TestExpression {
 	text: string;
-	invalid: 'false' | 'true' | 'semantic';
+	invalid: InvalidKind;
 }
 
 export interface TestLibrary {
 	text: string;
-	invalid: 'false' | 'true' | 'semantic';
+	invalid: InvalidKind;
 }
 
 export interface TestOutput {
@@ -89,7 +91,7 @@ export interface InternalTestResult {
 	testName: string;
 	testVersion?: string;
 	testVersionTo?: string;
-	invalid?: 'false' | 'true' | 'semantic' | 'undefined';
+	invalid?: ResultInvalidKind;
 	expression: string;
 	// For library-style tests: the full CQL library source, sent to Library/$evaluate wrapped as
 	// a FHIR Library resource. (For these tests, `expression` holds the name of the define whose
@@ -113,7 +115,7 @@ export interface TestResult {
 	testsName: string;
 	groupName: string;
 	testName: string;
-	invalid?: 'false' | 'true' | 'semantic';
+	invalid?: InvalidKind;
 	capabilities?: CapabilityKV[];
 	expression: string;
 }
diff --git a/src/shared/invalid-utils.ts b/src/shared/invalid-utils.ts
new file mode 100644
index 0000000..881fccf
--- /dev/null
+++ b/src/shared/invalid-utils.ts
@@ -0,0 +1,40 @@
+/**
+ * Semantics of the test schema's `invalid` attribute.
+ *
+ * `testSchema.xsd` defines five values for `InvalidType`, four of which say the test expects the
+ * engine to fail — they differ only in *how* it is expected to fail:
+ *
+ * - `false`     — the expression is expected to evaluate successfully
+ * - `syntax`    — expected to produce a syntax error (the translator rejects it)
+ * - `semantic`  — expected to produce a semantic error (the translator rejects it)
+ * - `execution` — expected to produce an execution error
+ * - `true`      — expected to produce a runtime error
+ *
+ * Treating only `true` and `semantic` as error-expecting scored a test as failed when the engine
+ * had in fact produced the syntax error the test asked for.
+ */
+export type InvalidKind = 'false' | 'syntax' | 'semantic' | 'execution' | 'true';
+
+/** `invalid` as recorded on a result, which also covers a test that declares no expression. */
+export type ResultInvalidKind = InvalidKind | 'undefined';
+
+const ERROR_EXPECTED: ReadonlySet<string> = new Set(['true', 'semantic', 'syntax', 'execution']);
+
+/**
+ * True when the test expects the engine to error, whatever kind of error that is. Such a test
+ * passes only if the engine actually errored, and needs no `<output>` to compare against.
+ */
+export function expectsError(invalid: string | undefined): boolean {
+	return invalid !== undefined && ERROR_EXPECTED.has(invalid);
+}
+
+const TRANSLATION_ERRORS: ReadonlySet<string> = new Set(['semantic', 'syntax']);
+
+/**
+ * True when the expression cannot survive CQL-to-ELM translation, so it must be left out of a
+ * generated library — one such define would fail the translation of every define around it.
+ * Runtime and execution errors translate fine and are kept.
+ */
+export function preventsTranslation(invalid: string | undefined): boolean {
+	return invalid !== undefined && TRANSLATION_ERRORS.has(invalid);
+}
diff --git a/src/shared/results-shared.ts b/src/shared/results-shared.ts
index f41e21d..56b4599 100644
--- a/src/shared/results-shared.ts
+++ b/src/shared/results-shared.ts
@@ -1,5 +1,7 @@
 import type { Tests, Test, InternalTestResult, CapabilityKV } from '../models/test-types.js';
 import type { Parameters } from 'fhir/r4';
+import { expectsError } from './invalid-utils.js';
+import type { ResultInvalidKind } from './invalid-utils.js';
 
 /**
  * The XML parser yields a bare object when an element declares exactly one <capability>
@@ -31,7 +33,7 @@ export class Result implements InternalTestResult {
 	testName: string;
 	testVersion?: string;
 	testVersionTo?: string;
-	invalid: 'false' | 'true' | 'semantic' | 'undefined';
+	invalid: ResultInvalidKind;
 	expression: string;
 	library?: string;
 	capability: CapabilityKV[] = [];
@@ -99,10 +101,10 @@ export class Result implements InternalTestResult {
 			} else {
 				this.expected = test.output as string;
 			}
-		} else if (this.invalid !== 'true' && this.invalid !== 'semantic') {
-			// No output is expected only when the expression is marked invalid ("true"
-			// for a run-time error, "semantic" for a translation error) — the test expects
-			// an error. Otherwise there is nothing to compare against, so skip.
+		} else if (!expectsError(this.invalid)) {
+			// No output is expected only when the expression is marked invalid — any of the four
+			// error kinds means the test expects the engine to fail. Otherwise there is nothing
+			// to compare against, so skip.
 			this.testStatus = 'skip';
 			this.skipMessage = 'No output specified';
 		}
diff --git a/src/shared/run-test-core.ts b/src/shared/run-test-core.ts
index c49b4a7..0303ece 100644
--- a/src/shared/run-test-core.ts
+++ b/src/shared/run-test-core.ts
@@ -12,6 +12,7 @@ import { resultsEqual } from './results-utils.js';
 import { formatActualValue } from '../test-results/cql-test-results.js';
 import { publishTestLibrary } from './library-publisher.js';
 import type { PublishedLibrary } from './library-publisher.js';
+import { expectsError } from './invalid-utils.js';
 
 /**
  * Shared execution state for a test run: the resolved config, the engine, the CVL parser,
@@ -121,8 +122,8 @@ function logSkip(result: InternalTestResult): void {
 /**
  * Runs a single test against the engine and records its outcome on `result`. Applies skip
  * precedence (pre-marked skip → OnlyList → config SkipList → version gating), then POSTs the
- * expression, extracts the actual value, and classifies pass/fail/error. Errors expected by
- * `invalid="true"/"semantic"` tests pass only when the engine actually erred.
+ * expression, extracts the actual value, and classifies pass/fail/error. A test whose `invalid`
+ * attribute names any of the four error kinds passes only when the engine actually erred.
  *
  * This is the single implementation shared by the CLI and server runners — both use `fetch` and
  * identical classification, so a test scores the same regardless of how it is invoked.
@@ -206,8 +207,10 @@ export async function runTest(
 		const invalid = result.invalid;
 		const erroredOut = responseIndicatesError(response.status, responseBody);
 
-		if (invalid === 'true' || invalid === 'semantic') {
-			// The expression is expected to error; it passes only if the engine erred.
+		if (expectsError(invalid)) {
+			// The expression is expected to error; it passes only if the engine erred. All four
+			// error kinds (syntax, semantic, execution, true) are treated alike here — the test
+			// asks for a failure, and the runner does not police which kind the engine produced.
 			result.testStatus = erroredOut ? 'pass' : 'fail';
 		} else if (!erroredOut) {
 			result.testStatus = resultsEqual(parsedExpected, result.actual) ? 'pass' : 'fail';
diff --git a/src/test-results/cql-test-results.ts b/src/test-results/cql-test-results.ts
index bb84124..01b9f59 100644
--- a/src/test-results/cql-test-results.ts
+++ b/src/test-results/cql-test-results.ts
@@ -5,6 +5,7 @@ import type { TestResult, InternalTestResult } from '../models/test-types.js';
 import type { TestResultsSummary, CQLTestResultsData } from '../models/results-types.js';
 import { ResultsValidator } from '../conf/results-validator.js';
 import { isIntervalShaped } from '../shared/interval-utils.js';
+import type { InvalidKind } from '../shared/invalid-utils.js';
 
 /**
  * Formats an actual value for report output. Structured CQL values are rendered in
@@ -209,7 +210,7 @@ export class CQLTestResults {
 				}),
 				...(result.invalid &&
 					result.invalid !== 'undefined' && {
-						invalid: result.invalid as 'false' | 'true' | 'semantic',
+						invalid: result.invalid as InvalidKind,
 					}),
 				...(result.capability &&
 					result.capability.length > 0 && { capabilities: result.capability }),
diff --git a/test/invalid-utils.test.ts b/test/invalid-utils.test.ts
new file mode 100644
index 0000000..506a473
--- /dev/null
+++ b/test/invalid-utils.test.ts
@@ -0,0 +1,72 @@
+import { describe, it, expect } from 'vitest';
+import { expectsError, preventsTranslation } from '../src/shared/invalid-utils.js';
+import { Result } from '../src/shared/results-shared.js';
+
+/**
+ * testSchema.xsd defines five InvalidType values. Four of them say the test expects the engine to
+ * fail; only `false` expects success.
+ */
+const ERROR_KINDS = ['true', 'semantic', 'syntax', 'execution'] as const;
+
+describe('expectsError', () => {
+	it('is true for every error kind the schema defines', () => {
+		for (const kind of ERROR_KINDS) {
+			expect(expectsError(kind), kind).toBe(true);
+		}
+	});
+
+	it('is false for a test expected to succeed, or with no invalid attribute', () => {
+		expect(expectsError('false')).toBe(false);
+		expect(expectsError(undefined)).toBe(false);
+		// The runner's own marker for a test that declares no expression at all.
+		expect(expectsError('undefined')).toBe(false);
+	});
+
+	it('is false for an unrecognised value rather than treating it as an error', () => {
+		expect(expectsError('nonsense')).toBe(false);
+		expect(expectsError('')).toBe(false);
+	});
+});
+
+describe('preventsTranslation', () => {
+	it('is true only for errors the translator raises', () => {
+		// A define that cannot translate would fail the whole generated library.
+		expect(preventsTranslation('syntax')).toBe(true);
+		expect(preventsTranslation('semantic')).toBe(true);
+	});
+
+	it('is false for run-time and execution errors, which translate fine', () => {
+		expect(preventsTranslation('true')).toBe(false);
+		expect(preventsTranslation('execution')).toBe(false);
+	});
+
+	it('is false for a valid expression or a missing attribute', () => {
+		expect(preventsTranslation('false')).toBe(false);
+		expect(preventsTranslation(undefined)).toBe(false);
+	});
+});
+
+describe('Result treats every error kind as needing no output', () => {
+	// A test that expects an error carries no <output>; before, only `true` and `semantic`
+	// were recognised, so a syntax-invalid test with no output was skipped as
+	// "No output specified" instead of being run.
+	for (const kind of ERROR_KINDS) {
+		it(`does not skip an invalid="${kind}" test that declares no output`, () => {
+			const result = new Result('T', 'G', {
+				name: 'ErrorExpected',
+				expression: { text: 'Ceiling(2147483648)', invalid: kind as any },
+			} as any);
+			expect(result.testStatus).not.toBe('skip');
+			expect(result.skipMessage).toBeUndefined();
+		});
+	}
+
+	it('still skips a valid test that declares no output', () => {
+		const result = new Result('T', 'G', {
+			name: 'NoOutput',
+			expression: '1 + 1',
+		} as any);
+		expect(result.testStatus).toBe('skip');
+		expect(result.skipMessage).toBe('No output specified');
+	});
+});