diff --git a/src/extractors/value-type-extractors/datetime-interval-extractor.ts b/src/extractors/value-type-extractors/datetime-interval-extractor.ts
index 83a1976..df7d643 100644
--- a/src/extractors/value-type-extractors/datetime-interval-extractor.ts
+++ b/src/extractors/value-type-extractors/datetime-interval-extractor.ts
@@ -37,25 +37,37 @@ const BOUNDARY_FORMATS = {
 
 export class DateTimeIntervalExtractor extends BaseExtractor {
 	protected _process(parameter: any): any {
-		if (parameter.hasOwnProperty('valuePeriod')) {
-			const format = BOUNDARY_FORMATS[declaredPointType(parameter) ?? 'DateTime'];
-			// Period boundaries are FHIR dateTimes, so a boundary coarser than seconds arrives
-			// zero-padded with its real precision on the `_start`/`_end` companion element.
-			const period = parameter.valuePeriod;
-			const low = period.hasOwnProperty('start')
-				? format(applyDeclaredTimePrecision(period.start, period._start))
-				: null;
-			const high = period.hasOwnProperty('end')
-				? format(applyDeclaredTimePrecision(period.end, period._end))
-				: null;
-			return {
-				lowClosed: low !== null,
-				low: low,
-				highClosed: true,
-				high: high,
-			};
+		if (!parameter.hasOwnProperty('valuePeriod')) {
+			return undefined;
 		}
 
-		return undefined;
+		const period = parameter.valuePeriod;
+		if (period === null || typeof period !== 'object') {
+			return undefined;
+		}
+
+		// With no cqf-cqlType the point type cannot be recovered: a Period boundary of
+		// `2012-01-01T00:00:00-07:00` is indistinguishable from a DateTime interval that starts at
+		// midnight. The IG requires the extension on every CQL-valued result and says a value
+		// without it is the FHIR type, so an undeclared Period is read as Interval<DateTime>.
+		const format = BOUNDARY_FORMATS[declaredPointType(parameter) ?? 'DateTime'];
+
+		// Period boundaries are FHIR dateTimes, so a boundary coarser than seconds arrives
+		// zero-padded with its real precision on the `_start`/`_end` companion element.
+		const low = period.hasOwnProperty('start')
+			? format(applyDeclaredTimePrecision(period.start, period._start))
+			: null;
+		const high = period.hasOwnProperty('end')
+			? format(applyDeclaredTimePrecision(period.end, period._end))
+			: null;
+
+		return {
+			lowClosed: low !== null,
+			low: low,
+			// An absent boundary is unbounded, so it is not closed. Matching
+			// NumericIntervalExtractor keeps `Interval[x, null)` comparable either way it arrives.
+			highClosed: high !== null,
+			high: high,
+		};
 	}
 }
diff --git a/src/extractors/value-type-extractors/quantity-interval-extractor.ts b/src/extractors/value-type-extractors/quantity-interval-extractor.ts
index 56367ab..6d45dcc 100644
--- a/src/extractors/value-type-extractors/quantity-interval-extractor.ts
+++ b/src/extractors/value-type-extractors/quantity-interval-extractor.ts
@@ -1,35 +1,50 @@
 import { BaseExtractor } from '../base-extractor.js';
 
+/**
+ * A Range boundary as the CQL Quantity shape CVL produces: `{value, unit}`.
+ *
+ * The unit is taken from `Quantity.code` — the coded, comparable form — falling back to
+ * `Quantity.unit` when a boundary carries only the human-readable unit, so a dimensioned
+ * boundary is not silently reduced to a unitless one. A boundary that is absent, not an object,
+ * or carries no `value` is treated as no boundary at all rather than throwing.
+ */
+function boundaryQuantity(value: any): { value: any; unit: any } | null {
+	if (value === null || typeof value !== 'object' || !value.hasOwnProperty('value')) {
+		return null;
+	}
+	const unit = value.hasOwnProperty('code')
+		? value.code
+		: value.hasOwnProperty('unit')
+			? value.unit
+			: null;
+	return { value: value.value, unit: unit };
+}
+
+/**
+ * Extracts a `valueRange` as an `Interval<Quantity>`. This is the fallback for any Range that
+ * NumericIntervalExtractor did not claim: per the IG a result carrying no `cqf-cqlType` is read as
+ * the FHIR type, and the CQL type mapped to `FHIR.Range` with quantity boundaries is
+ * `Interval<Quantity>`.
+ */
 export class QuantityIntervalExtractor extends BaseExtractor {
 	protected _process(parameter: any): any {
-		function getQuantity(value: any): any {
-			if (value.hasOwnProperty('value')) {
-				return {
-					value: value.value,
-					unit: value.hasOwnProperty('code') ? value.code : null,
-				};
-			}
-
-			return null;
+		if (!parameter.hasOwnProperty('valueRange')) {
+			return undefined;
 		}
 
-		if (parameter.hasOwnProperty('valueRange')) {
-			const low = parameter.valueRange.hasOwnProperty('low')
-				? getQuantity(parameter.valueRange.low)
-				: null;
-
-			const high = parameter.valueRange.hasOwnProperty('high')
-				? getQuantity(parameter.valueRange.high)
-				: null;
-
-			return {
-				lowClosed: low !== null,
-				low: low,
-				highClosed: high !== null,
-				high: high,
-			};
+		const range = parameter.valueRange;
+		if (range === null || typeof range !== 'object') {
+			return undefined;
 		}
 
-		return undefined;
+		const low = range.hasOwnProperty('low') ? boundaryQuantity(range.low) : null;
+		const high = range.hasOwnProperty('high') ? boundaryQuantity(range.high) : null;
+
+		return {
+			lowClosed: low !== null,
+			low: low,
+			highClosed: high !== null,
+			high: high,
+		};
 	}
 }
diff --git a/test/interval-fhir-types.test.ts b/test/interval-fhir-types.test.ts
new file mode 100644
index 0000000..8da7fa5
--- /dev/null
+++ b/test/interval-fhir-types.test.ts
@@ -0,0 +1,182 @@
+import { describe, it, expect, beforeAll } from 'vitest';
+import { buildExtractor } from '../src/server/extractor-builder.js';
+import { resultsEqual } from '../src/shared/results-utils.js';
+import { ValueMap } from '../src/extractors/value-map.js';
+
+/**
+ * Covers the FHIR types the "Using CQL with FHIR" IG maps intervals onto (Conformance
+ * Requirement 4.3): Interval<Integer|Long|Decimal|Quantity> as FHIR.Range and
+ * Interval<Date|DateTime|Time> as FHIR.Period.
+ */
+const CQL_TYPE_URL = 'http://hl7.org/fhir/StructureDefinition/cqf-cqlType';
+
+let cvl: any;
+let extractor: ReturnType<typeof buildExtractor>;
+
+beforeAll(async () => {
+	// @ts-expect-error - cvl.mjs has no declaration file
+	cvl = (await import('../cvl/cvl.mjs')).default;
+	extractor = buildExtractor();
+});
+
+function parameters(parameter: any) {
+	return { resourceType: 'Parameters', parameter: [parameter] };
+}
+
+/** Extracts a single-parameter response the way runTest does, given the expected CQL literal. */
+function extractFor(parameter: any, expectedLiteral: string) {
+	const expected = cvl.parse(expectedLiteral);
+	const actual = extractor.extract(parameters(parameter), {
+		singletonListKeys: ValueMap.singletonListKeysFromExpected(expected),
+	});
+	return { expected, actual };
+}
+
+function cqlType(type: string) {
+	return { extension: [{ url: CQL_TYPE_URL, valueString: type }] };
+}
+
+describe('Interval<Integer|Decimal> as FHIR.Range', () => {
+	it('matches an Integer interval declared by cqf-cqlType', () => {
+		const { expected, actual } = extractFor(
+			{
+				name: 'return',
+				...cqlType('Interval<System.Integer>'),
+				valueRange: { low: { value: 1 }, high: { value: 10 } },
+			},
+			'Interval[1, 10]'
+		);
+		expect(resultsEqual(expected, actual)).toBe(true);
+	});
+
+	it('matches a Decimal interval declared by cqf-cqlType', () => {
+		const { expected, actual } = extractFor(
+			{
+				name: 'return',
+				...cqlType('Interval<System.Decimal>'),
+				valueRange: { low: { value: 1.0 }, high: { value: 10.0 } },
+			},
+			'Interval[1.0, 10.0]'
+		);
+		expect(resultsEqual(expected, actual)).toBe(true);
+	});
+
+	it('yields plain numbers, not quantities, for a numeric interval', () => {
+		const { actual } = extractFor(
+			{
+				name: 'return',
+				...cqlType('Interval<System.Integer>'),
+				valueRange: { low: { value: 1 }, high: { value: 10 } },
+			},
+			'Interval[1, 10]'
+		);
+		expect(actual).toEqual({ lowClosed: true, low: 1, highClosed: true, high: 10 });
+	});
+});
+
+describe('Interval<Quantity> as FHIR.Range', () => {
+	it('matches a dimensioned quantity interval', () => {
+		const { expected, actual } = extractFor(
+			{
+				name: 'return',
+				valueRange: {
+					low: { value: 1, unit: 'mg', system: 'http://unitsofmeasure.org', code: 'mg' },
+					high: { value: 10, unit: 'mg', system: 'http://unitsofmeasure.org', code: 'mg' },
+				},
+			},
+			"Interval[1 'mg', 10 'mg']"
+		);
+		expect(resultsEqual(expected, actual)).toBe(true);
+	});
+
+	it('falls back to Quantity.unit when a boundary carries no code', () => {
+		// Otherwise a dimensioned boundary is silently reduced to a unitless one.
+		const { expected, actual } = extractFor(
+			{
+				name: 'return',
+				valueRange: { low: { value: 1, unit: 'mg' }, high: { value: 10, unit: 'mg' } },
+			},
+			"Interval[1 'mg', 10 'mg']"
+		);
+		expect(resultsEqual(expected, actual)).toBe(true);
+	});
+});
+
+describe('Interval<Date|DateTime|Time> as FHIR.Period', () => {
+	it('matches a Date interval declared by cqf-cqlType', () => {
+		const { expected, actual } = extractFor(
+			{
+				name: 'return',
+				...cqlType('Interval<System.Date>'),
+				valuePeriod: { start: '2012-01-01T00:00:00-07:00', end: '2012-12-31T00:00:00-07:00' },
+			},
+			'Interval[@2012-01-01, @2012-12-31]'
+		);
+		expect(resultsEqual(expected, actual)).toBe(true);
+	});
+
+	it('matches a Time interval anchored to the placeholder date', () => {
+		// The IG maps Interval<Time> onto a Period whose boundaries are dateTimes anchored to
+		// @0001-01-01; the date and any offset are artifacts of that mapping.
+		const { expected, actual } = extractFor(
+			{
+				name: 'return',
+				...cqlType('Interval<System.Time>'),
+				valuePeriod: { start: '0001-01-01T01:00:00.000Z', end: '0001-01-01T02:00:00.000Z' },
+			},
+			'Interval[@T01:00:00.000, @T02:00:00.000]'
+		);
+		expect(resultsEqual(expected, actual)).toBe(true);
+	});
+
+	it('reads an undeclared Period as Interval<DateTime>, per the IG', () => {
+		// Without cqf-cqlType the point type cannot be recovered, and the IG says a value with no
+		// cqlType is the FHIR type. This documents that a Date interval returned without the
+		// extension does NOT match — the omission is the server's to fix, not something to guess at.
+		const { expected, actual } = extractFor(
+			{
+				name: 'return',
+				valuePeriod: { start: '2012-01-01T00:00:00-07:00', end: '2012-12-31T00:00:00-07:00' },
+			},
+			'Interval[@2012-01-01, @2012-12-31]'
+		);
+		expect(resultsEqual(expected, actual)).toBe(false);
+	});
+});
+
+describe('boundary and robustness handling', () => {
+	it('treats an absent Period end as an unbounded, open high boundary', () => {
+		const actual = extractor.extract(
+			parameters({ name: 'return', valuePeriod: { start: '2012-01-01' } })
+		);
+		expect(actual).toMatchObject({ highClosed: false, high: null });
+	});
+
+	it('treats an absent Range high the same way', () => {
+		const actual = extractor.extract(
+			parameters({ name: 'return', valueRange: { low: { value: 1, code: 'mg' } } })
+		);
+		expect(actual).toMatchObject({ highClosed: false, high: null });
+	});
+
+	it('does not throw on a null valuePeriod, valueRange or boundary', () => {
+		expect(() =>
+			extractor.extract(parameters({ name: 'return', valuePeriod: null }))
+		).not.toThrow();
+		expect(() =>
+			extractor.extract(parameters({ name: 'return', valueRange: null }))
+		).not.toThrow();
+		expect(() =>
+			extractor.extract(
+				parameters({ name: 'return', valueRange: { low: null, high: { value: 10, code: 'mg' } } })
+			)
+		).not.toThrow();
+	});
+
+	it('treats a boundary with no value as no boundary', () => {
+		const actual = extractor.extract(
+			parameters({ name: 'return', valueRange: { low: {}, high: { value: 10, code: 'mg' } } })
+		);
+		expect(actual).toMatchObject({ lowClosed: false, low: null });
+	});
+});