diff --git a/spring-core/src/main/java/org/springframework/aot/hint/SimpleTypeReference.java b/spring-core/src/main/java/org/springframework/aot/hint/SimpleTypeReference.java
index 9d7300f45e8..7105738d91c 100644
--- a/spring-core/src/main/java/org/springframework/aot/hint/SimpleTypeReference.java
+++ b/spring-core/src/main/java/org/springframework/aot/hint/SimpleTypeReference.java
@@ -16,6 +16,8 @@
 
 package org.springframework.aot.hint;
 
+import javax.lang.model.SourceVersion;
+
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
@@ -26,6 +28,7 @@ import org.springframework.util.Assert;
  */
 final class SimpleTypeReference extends AbstractTypeReference {
 
+	@Nullable
 	private String canonicalName;
 
 	private final String packageName;
@@ -44,6 +47,9 @@ final class SimpleTypeReference extends AbstractTypeReference {
 
 	static SimpleTypeReference of(String className) {
 		Assert.notNull(className, "ClassName must not be null");
+		if (!isValidClassName(className)) {
+			throw new IllegalStateException("Invalid class name '" + className + "'");
+		}
 		if (!className.contains("$")) {
 			return createTypeReference(className);
 		}
@@ -55,9 +61,19 @@ final class SimpleTypeReference extends AbstractTypeReference {
 		return typeReference;
 	}
 
+	private static boolean isValidClassName(String className) {
+		for (String s : className.split("\\.", -1)) {
+			if (!SourceVersion.isIdentifier(s)) {
+				return false;
+			}
+		}
+		return true;
+	}
+
 	private static SimpleTypeReference createTypeReference(String className) {
 		int i = className.lastIndexOf('.');
-		return new SimpleTypeReference(className.substring(0, i), className.substring(i + 1), null);
+		return (i != -1 ? new SimpleTypeReference(className.substring(0, i), className.substring(i + 1), null)
+				: new SimpleTypeReference("", className, null));
 	}
 
 	@Override
@@ -65,12 +81,13 @@ final class SimpleTypeReference extends AbstractTypeReference {
 		if (this.canonicalName == null) {
 			StringBuilder names = new StringBuilder();
 			buildName(this, names);
-			this.canonicalName = this.packageName + "." + names;
+			this.canonicalName = (this.packageName.isEmpty()
+					? names.toString() : this.packageName + "." + names);
 		}
 		return this.canonicalName;
 	}
 
-	private static void buildName(TypeReference type, StringBuilder sb) {
+	private static void buildName(@Nullable TypeReference type, StringBuilder sb) {
 		if (type == null) {
 			return;
 		}
diff --git a/spring-core/src/test/java/org/springframework/aot/hint/SimpleTypeReferenceTests.java b/spring-core/src/test/java/org/springframework/aot/hint/SimpleTypeReferenceTests.java
new file mode 100644
index 00000000000..6ce3fb68a30
--- /dev/null
+++ b/spring-core/src/test/java/org/springframework/aot/hint/SimpleTypeReferenceTests.java
@@ -0,0 +1,47 @@
+/*
+ * Copyright 2002-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.aot.hint;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
+
+/**
+ * Tests for {@link SimpleTypeReference}.
+ *
+ * @author Stephane Nicoll
+ */
+class SimpleTypeReferenceTests {
+
+	@Test
+	void typeReferenceInRootPackage() {
+		TypeReference type = SimpleTypeReference.of("MyRootClass");
+		assertThat(type.getCanonicalName()).isEqualTo("MyRootClass");
+		assertThat(type.getPackageName()).isEqualTo("");
+	}
+
+	@ParameterizedTest(name = "{0}")
+	@ValueSource(strings = { "com.example.Tes(t", "com.example..Test" })
+	void typeReferenceWithInvalidClassName(String invalidClassName) {
+		assertThatIllegalStateException().isThrownBy(() -> SimpleTypeReference.of(invalidClassName))
+				.withMessageContaining("Invalid class name");
+	}
+
+}