diff --git a/CHANGELOG.md b/CHANGELOG.md
index 57070b9..41b8da0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Changed
+- `weaver-pojo-serde-extension`: Slightly changed the `SerdePojoReaderWriterSpec`
+  to be more closely aligned with Java's identifier rules.
+
 ## [0.7.0] - 2025-12-19
 
 ### Changed
diff --git a/tweed5/weaver-pojo-serde-extension/src/main/java/de/siphalor/tweed5/weaver/pojoext/serde/impl/SerdePojoReaderWriterSpec.java b/tweed5/weaver-pojo-serde-extension/src/main/java/de/siphalor/tweed5/weaver/pojoext/serde/impl/SerdePojoReaderWriterSpec.java
index a5fc31d..8bd2b19 100644
--- a/tweed5/weaver-pojo-serde-extension/src/main/java/de/siphalor/tweed5/weaver/pojoext/serde/impl/SerdePojoReaderWriterSpec.java
+++ b/tweed5/weaver-pojo-serde-extension/src/main/java/de/siphalor/tweed5/weaver/pojoext/serde/impl/SerdePojoReaderWriterSpec.java
@@ -7,6 +7,18 @@ import java.util.Collections;
 import java.util.List;
 import java.util.PrimitiveIterator;
 
+/**
+ * Specification describing how to construct a reader or writer.
+ * <p>
+ * The formal syntax is:
+ * <code><pre>
+ * &lt;spec&gt; ::= &lt;identifier&gt; [ '(' &lt;spec-list&gt; ')' ]
+ * &lt;spec-list&gt; ::= &lt;spec&gt; [ ',' &lt;spec-list&gt; ]
+ * &lt;identifier&gt; ::= &lt;identifier-part&gt; [ '.' &lt;identifier&gt; ]
+ * &lt;identifier-part&gt; ::= ( &lt;alpha&gt; | '_' ) [ &lt;alphanumeric-identifier-part&gt; ]
+ * &lt;alphanumeric-identifier-part&gt; ::= ( &lt;alphanumeric&gt; | '_' ) [ &lt;alphanumeric-identifier-part&gt; ]
+ * </pre></code>
+ */
 @Value
 public class SerdePojoReaderWriterSpec {
 	String identifier;
@@ -71,14 +83,14 @@ public class SerdePojoReaderWriterSpec {
 			int codePoint = nextCodePoint();
 			if (codePoint == -1) {
 				throw createException("Expected identifier, got end of input", codePoint);
-			} else if (!isIdentifierChar(codePoint)) {
+			} else if (!isIdentifierStart(codePoint)) {
 				throw createException("Expected identifier (alphanumeric character)", codePoint);
 			}
 			StringBuilder stringBuilder = new StringBuilder();
 			stringBuilder.appendCodePoint(codePoint);
 			boolean dot = false;
 			while ((codePoint = peekCodePoint()) >= 0) {
-				if (isIdentifierChar(codePoint)) {
+				if (isIdentifierPart(codePoint)) {
 					stringBuilder.appendCodePoint(nextCodePoint());
 					dot = false;
 				} else if (codePoint == '.') {
@@ -98,9 +110,20 @@ public class SerdePojoReaderWriterSpec {
 			return stringBuilder.toString();
 		}
 
-		private boolean isIdentifierChar(int codePoint) {
-			return (codePoint >= '0' && codePoint <= '9')
-					|| (codePoint >= 'a' && codePoint <= 'z')
+		private boolean isIdentifierStart(int codePoint) {
+			return isAlpha(codePoint) || codePoint == '_';
+		}
+
+		private boolean isIdentifierPart(int codePoint) {
+			return isAlphanumeric(codePoint) || codePoint == '_';
+		}
+
+		private boolean isAlphanumeric(int codePoint) {
+			return (codePoint >= '0' && codePoint <= '9') || isAlpha(codePoint);
+		}
+
+		private boolean isAlpha(int codePoint) {
+			return (codePoint >= 'a' && codePoint <= 'z')
 					|| (codePoint >= 'A' && codePoint <= 'Z');
 		}
 
@@ -167,4 +190,4 @@ public class SerdePojoReaderWriterSpec {
 					.toString();
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/tweed5/weaver-pojo-serde-extension/src/test/java/de/siphalor/tweed5/weaver/pojoext/serde/impl/SerdePojoReaderWriterSpecTest.java b/tweed5/weaver-pojo-serde-extension/src/test/java/de/siphalor/tweed5/weaver/pojoext/serde/impl/SerdePojoReaderWriterSpecTest.java
index 8f6aa0b..22b60a5 100644
--- a/tweed5/weaver-pojo-serde-extension/src/test/java/de/siphalor/tweed5/weaver/pojoext/serde/impl/SerdePojoReaderWriterSpecTest.java
+++ b/tweed5/weaver-pojo-serde-extension/src/test/java/de/siphalor/tweed5/weaver/pojoext/serde/impl/SerdePojoReaderWriterSpecTest.java
@@ -20,7 +20,8 @@ class SerdePojoReaderWriterSpecTest {
 			"  abc()  ,abc",
 			"  abc.123  ,abc.123",
 			"abc.123  (  )  ,abc.123",
-			"123.abc,123.abc",
+			"_123._123,_123._123",
+			"ab_cd,ab_cd",
 	})
 	@SneakyThrows
 	void parseSimpleIdentifier(String input, String identifier) {
@@ -32,9 +33,9 @@ class SerdePojoReaderWriterSpecTest {
 	@Test
 	@SneakyThrows
 	void parseNested() {
-		SerdePojoReaderWriterSpec spec = SerdePojoReaderWriterSpec.parse("abc.def ( 12 ( def, ghi ( ) ), jkl ) ");
+		SerdePojoReaderWriterSpec spec = SerdePojoReaderWriterSpec.parse("abc.def ( _12 ( def, ghi ( ) ), jkl ) ");
 		assertThat(spec).isEqualTo(new SerdePojoReaderWriterSpec("abc.def", Arrays.asList(
-				new SerdePojoReaderWriterSpec("12", Arrays.asList(
+				new SerdePojoReaderWriterSpec("_12", Arrays.asList(
 						new SerdePojoReaderWriterSpec("def", Collections.emptyList()),
 						new SerdePojoReaderWriterSpec("ghi", Collections.emptyList())
 				)),
@@ -51,6 +52,7 @@ class SerdePojoReaderWriterSpecTest {
 			",;1;,",
 			"abc(,);5;,",
 			"abc..def;5;.",
+			"123.abc;1;1",
 	})
 	@SneakyThrows
 	void parseError(String input, int index, @Nullable String codePoint) {