diff --git a/src/main/java/core/packetproxy/model/Modification.java b/src/main/java/core/packetproxy/model/Modification.java
index df90b77..41f39fd 100644
--- a/src/main/java/core/packetproxy/model/Modification.java
+++ b/src/main/java/core/packetproxy/model/Modification.java
@@ -129,10 +129,16 @@ private byte[] replaceRegex(byte[] data, Packet packet) {
 		Pattern pattern = Pattern.compile(this.pattern, Pattern.MULTILINE);
 		Matcher matcher = pattern.matcher(new String(data));
 		String result = new String(data);
+		boolean matched = false;
 		while (matcher.find()) {
+			matched = true;
 			result = matcher.replaceAll(this.replaced);
 			packet.setModified();
 		}
+		if (!matched) {
+			// バイナリデータが壊れる可能性があるので、マッチしなかった場合はそのまま返す
+			return data;
+		}
 		return result.getBytes();
 	}
 	private byte[] replaceBinary(byte[] data, Packet packet) throws Exception {