diff --git a/spring-restdocs-core/src/main/java/org/springframework/restdocs/operation/preprocess/PatternReplacingContentModifier.java b/spring-restdocs-core/src/main/java/org/springframework/restdocs/operation/preprocess/PatternReplacingContentModifier.java
index d0b9f4a2..1c70d3a3 100644
--- a/spring-restdocs-core/src/main/java/org/springframework/restdocs/operation/preprocess/PatternReplacingContentModifier.java
+++ b/spring-restdocs-core/src/main/java/org/springframework/restdocs/operation/preprocess/PatternReplacingContentModifier.java
@@ -65,6 +65,9 @@ public byte[] modifyContent(byte[] content, @Nullable MediaType contentType) {
 		while (matcher.find()) {
 			String prefix;
 			if (matcher.groupCount() > 0) {
+				if (matcher.start(1) == -1) {
+					continue;
+				}
 				prefix = original.substring(previous, matcher.start(1));
 				previous = matcher.end(1);
 			}
diff --git a/spring-restdocs-core/src/test/java/org/springframework/restdocs/operation/preprocess/PatternReplacingContentModifierTests.java b/spring-restdocs-core/src/test/java/org/springframework/restdocs/operation/preprocess/PatternReplacingContentModifierTests.java
index 6865eeec..d6399f58 100644
--- a/spring-restdocs-core/src/test/java/org/springframework/restdocs/operation/preprocess/PatternReplacingContentModifierTests.java
+++ b/spring-restdocs-core/src/test/java/org/springframework/restdocs/operation/preprocess/PatternReplacingContentModifierTests.java
@@ -40,6 +40,30 @@ void contentThatDoesNotMatchIsUnchanged() {
 			.isEqualTo("{\"id\" : \"CA76-ED42-11CE-BACD\"}".getBytes());
 	}
 
+	@Test
+	void whenPatternHasAGroupOnlyTheFirstGroupIsReplaced() {
+		Pattern pattern = Pattern.compile("\"id\":\"([^\"]+)\"");
+		PatternReplacingContentModifier contentModifier = new PatternReplacingContentModifier(pattern, "<<id>>");
+		assertThat(contentModifier.modifyContent("{\"id\":\"abc\",\"name\":\"alpha\"}".getBytes(), null))
+			.isEqualTo("{\"id\":\"<<id>>\",\"name\":\"alpha\"}".getBytes());
+	}
+
+	@Test
+	void matchInWhichTheFirstGroupDoesNotParticipateIsUnchanged() {
+		Pattern pattern = Pattern.compile("\"id\":\"([^\"]+)\"|\"created\":\"[^\"]+\"");
+		PatternReplacingContentModifier contentModifier = new PatternReplacingContentModifier(pattern, "<<masked>>");
+		assertThat(contentModifier.modifyContent("{\"created\":\"2026-10-16\",\"id\":\"abc\"}".getBytes(), null))
+			.isEqualTo("{\"created\":\"2026-10-16\",\"id\":\"<<masked>>\"}".getBytes());
+	}
+
+	@Test
+	void matchInWhichAnOptionalFirstGroupIsAbsentIsUnchanged() {
+		Pattern pattern = Pattern.compile("[0-9]+(-SNAPSHOT)?");
+		PatternReplacingContentModifier contentModifier = new PatternReplacingContentModifier(pattern, "-RELEASE");
+		assertThat(contentModifier.modifyContent("1.0 2.0-SNAPSHOT".getBytes(), null))
+			.isEqualTo("1.0 2.0-RELEASE".getBytes());
+	}
+
 	@Test
 	void encodingIsPreservedUsingCharsetFromContentType() {
 		String japaneseContent = "\u30b3\u30f3\u30c6\u30f3\u30c4";