diff --git a/spring-core/src/jmh/java/org/springframework/core/env/CompositePropertySourceBenchmark.java b/spring-core/src/jmh/java/org/springframework/core/env/CompositePropertySourceBenchmark.java
new file mode 100644
index 00000000000..3d5eae2bdf5
--- /dev/null
+++ b/spring-core/src/jmh/java/org/springframework/core/env/CompositePropertySourceBenchmark.java
@@ -0,0 +1,85 @@
+/*
+ * Copyright 2002-2023 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.core.env;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Level;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+import org.openjdk.jmh.infra.Blackhole;
+
+import org.springframework.util.AlternativeJdkIdGenerator;
+import org.springframework.util.IdGenerator;
+
+/**
+ * Benchmarks for {@link CompositePropertySource}.
+ *
+ * @author Yike Xiao
+ */
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Warmup(iterations = 5, time = 2)
+@Measurement(iterations = 5, time = 2)
+public class CompositePropertySourceBenchmark {
+
+	@Benchmark
+	public void getPropertyNames(BenchmarkState state, Blackhole blackhole) {
+		blackhole.consume(state.composite.getPropertyNames());
+	}
+
+	@State(Scope.Benchmark)
+	public static class BenchmarkState {
+
+		private static final IdGenerator ID_GENERATOR = new AlternativeJdkIdGenerator();
+
+		private static final Object VALUE = new Object();
+
+		CompositePropertySource composite;
+
+		@Param({ "2", "5", "10" })
+		int numberOfPropertySource;
+
+		@Param({ "10", "100", "1000" })
+		int numberOfPropertyNamesPerSource;
+
+		@Setup(Level.Trial)
+		public void setUp() {
+			this.composite = new CompositePropertySource("benchmark");
+			for (int i = 0; i < this.numberOfPropertySource; i++) {
+				Map<String, Object> map = new HashMap<>(this.numberOfPropertyNamesPerSource);
+				for (int j = 0; j < this.numberOfPropertyNamesPerSource; j++) {
+					map.put(ID_GENERATOR.generateId().toString(), VALUE);
+				}
+				PropertySource<?> propertySource = new MapPropertySource("propertySource" + i, map);
+				this.composite.addPropertySource(propertySource);
+			}
+		}
+
+	}
+
+}
diff --git a/spring-core/src/main/java/org/springframework/core/env/CompositePropertySource.java b/spring-core/src/main/java/org/springframework/core/env/CompositePropertySource.java
index 6224a95f339..7345ff4dff9 100644
--- a/spring-core/src/main/java/org/springframework/core/env/CompositePropertySource.java
+++ b/spring-core/src/main/java/org/springframework/core/env/CompositePropertySource.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -78,15 +78,20 @@ public class CompositePropertySource extends EnumerablePropertySource<Object> {
 
 	@Override
 	public String[] getPropertyNames() {
-		Set<String> names = new LinkedHashSet<>();
+		List<String[]> namesList = new ArrayList<>(this.propertySources.size());
+		int total = 0;
 		for (PropertySource<?> propertySource : this.propertySources) {
 			if (!(propertySource instanceof EnumerablePropertySource<?> enumerablePropertySource)) {
 				throw new IllegalStateException(
 						"Failed to enumerate property names due to non-enumerable property source: " + propertySource);
 			}
-			names.addAll(Arrays.asList(enumerablePropertySource.getPropertyNames()));
+			String[] names = enumerablePropertySource.getPropertyNames();
+			namesList.add(names);
+			total += names.length;
 		}
-		return StringUtils.toStringArray(names);
+		Set<String> allNames = new LinkedHashSet<>(total);
+		namesList.forEach(names -> allNames.addAll(Arrays.asList(names)));
+		return StringUtils.toStringArray(allNames);
 	}
 
 
diff --git a/spring-core/src/test/java/org/springframework/core/env/CompositePropertySourceTests.java b/spring-core/src/test/java/org/springframework/core/env/CompositePropertySourceTests.java
index d7bafe37643..fba8bd2aa5d 100644
--- a/spring-core/src/test/java/org/springframework/core/env/CompositePropertySourceTests.java
+++ b/spring-core/src/test/java/org/springframework/core/env/CompositePropertySourceTests.java
@@ -17,6 +17,7 @@
 package org.springframework.core.env;
 
 import java.util.Collections;
+import java.util.Map;
 
 import org.junit.jupiter.api.Test;
 
@@ -46,4 +47,13 @@ class CompositePropertySourceTests {
 		assertThat(((i1 < i2) && (i2 < i3))).as("Bad order: " + s).isTrue();
 	}
 
+	@Test
+	void getPropertyNamesRemovesDuplicates() {
+		CompositePropertySource composite = new CompositePropertySource("c");
+		composite.addPropertySource(new MapPropertySource("p1", Map.of("p1.property", "value")));
+		composite.addPropertySource(new MapPropertySource("p2",
+				Map.of("p2.property1", "value", "p1.property", "value", "p2.property2", "value")));
+		assertThat(composite.getPropertyNames()).containsOnly("p1.property", "p2.property1", "p2.property2");
+	}
+
 }