diff --git a/source/lib/parser.ts b/source/lib/parser.ts
index 5b72a06c..8ad952f4 100644
--- a/source/lib/parser.ts
+++ b/source/lib/parser.ts
@@ -14,33 +14,47 @@ export const extractAssertions = (program: Program): Map<Assertion, Set<CallExpr
 	const checker = program.getTypeChecker();
 
 	/**
-	 * Recursively loop over all the nodes and extract all the assertions out of the source files.
+	 * Checks if the given node is semantically valid and is an assertion.
 	 */
-	function walkNodes(node: Node) {
-		if (isCallExpression(node)) {
-			const expression = isPropertyAccessExpression(node.expression) ?
-				node.expression.name :
-				node.expression;
+	function handleNode(node: CallExpression) {
+		const expression = isPropertyAccessExpression(node.expression) ?
+			node.expression.name :
+			node.expression;
+
+		const maybeSymbol = checker.getSymbolAtLocation(expression);
+
+		if (!maybeSymbol) {
+			// Bail out if a Symbol doesn't exist for this Node
+			// This either means a symbol could not be resolved
+			// for an identifier, or that the expression is
+			// syntactically valid, but not semantically valid.
+			return;
+		}
+
+		const symbol = maybeSymbol.flags & SymbolFlags.Alias ?
+			checker.getAliasedSymbol(maybeSymbol) :
+			maybeSymbol;
 
-			const maybeAlias = checker.getSymbolAtLocation(expression);
-			if (maybeAlias) {
-				const symbol = maybeAlias.flags & SymbolFlags.Alias ?
-					checker.getAliasedSymbol(maybeAlias) :
-					maybeAlias;
+		const identifier = symbol.getName();
 
-				const identifier = symbol.getName();
+		// Check if the call type is a valid assertion
+		if (assertionFnNames.has(identifier)) {
+			const assertion = identifier as Assertion;
 
-				// Check if the call type is a valid assertion
-				if (assertionFnNames.has(identifier)) {
-					const assertion = identifier as Assertion;
+			const nodes = assertions.get(assertion) ?? new Set<CallExpression>();
 
-					const nodes = assertions.get(assertion) ?? new Set<CallExpression>();
+			nodes.add(node);
 
-					nodes.add(node);
+			assertions.set(assertion, nodes);
+		}
+	}
 
-					assertions.set(assertion, nodes);
-				}
-			}
+	/**
+	 * Recursively loop over all the nodes and extract all the assertions out of the source files.
+	 */
+	function walkNodes(node: Node) {
+		if (isCallExpression(node)) {
+			handleNode(node);
 		}
 
 		forEachChild(node, walkNodes);
diff --git a/source/test/fixtures/undefined-symbol/index.d.ts b/source/test/fixtures/undefined-symbol/index.d.ts
new file mode 100644
index 00000000..336ce12b
--- /dev/null
+++ b/source/test/fixtures/undefined-symbol/index.d.ts
@@ -0,0 +1 @@
+export {}
diff --git a/source/test/fixtures/undefined-symbol/index.test-d.ts b/source/test/fixtures/undefined-symbol/index.test-d.ts
new file mode 100644
index 00000000..810a76b8
--- /dev/null
+++ b/source/test/fixtures/undefined-symbol/index.test-d.ts
@@ -0,0 +1,7 @@
+import {expectType} from '../../../..';
+
+// Identifier `bar` has no Symbol
+const anyCall = (foo: any) => foo.bar();
+
+// Fails with `Cannot read properties of undefined (reading 'flags')` in 0.24.0
+expectType<any>(anyCall('foo'));
diff --git a/source/test/fixtures/undefined-symbol/package.json b/source/test/fixtures/undefined-symbol/package.json
new file mode 100644
index 00000000..de6dc1db
--- /dev/null
+++ b/source/test/fixtures/undefined-symbol/package.json
@@ -0,0 +1,3 @@
+{
+	"name": "foo"
+}
diff --git a/source/test/test.ts b/source/test/test.ts
index 21ad2930..b29f9063 100644
--- a/source/test/test.ts
+++ b/source/test/test.ts
@@ -466,3 +466,9 @@ test('assertions should be identified if aliased', async t => {
 
 	verify(t, diagnostics, []);
 });
+
+test('parsing undefined symbol should not fail', async t => {
+	const diagnostics = await tsd({cwd: path.join(__dirname, 'fixtures/undefined-symbol')});
+
+	verify(t, diagnostics, []);
+});