diff --git a/code-generator/pom.xml b/code-generator/pom.xml
index ad623f1..9e33b25 100644
--- a/code-generator/pom.xml
+++ b/code-generator/pom.xml
@@ -41,11 +41,6 @@
             <artifactId>slf4j-api</artifactId>
         </dependency>
 
-        <dependency>
-            <groupId>com.google.guava</groupId>
-            <artifactId>guava</artifactId>
-        </dependency>
-
         <dependency>
             <groupId>org.jboss.forge.roaster</groupId>
             <artifactId>roaster-api</artifactId>
diff --git a/code-generator/src/main/java/io/streamnative/lightproto/generator/LightProtoGenerator.java b/code-generator/src/main/java/io/streamnative/lightproto/generator/LightProtoGenerator.java
index 5689d1b..c8f4a2a 100644
--- a/code-generator/src/main/java/io/streamnative/lightproto/generator/LightProtoGenerator.java
+++ b/code-generator/src/main/java/io/streamnative/lightproto/generator/LightProtoGenerator.java
@@ -15,7 +15,6 @@
  */
 package io.streamnative.lightproto.generator;
 
-import com.google.common.base.Joiner;
 import org.jboss.forge.roaster.Roaster;
 import org.jboss.forge.roaster.model.source.JavaClassSource;
 import org.slf4j.Logger;
@@ -79,7 +78,7 @@ public static List<File> generate(List<ProtoFileDescriptor> descriptors, File ou
             String outerClassName = Util.camelCaseFirstUpper(classPrefix, fileWithoutExtension);
 
             String javaPackageName = proto.getJavaPackageName();
-            String javaDir = Joiner.on('/').join(javaPackageName.split("\\."));
+            String javaDir = String.join("/", javaPackageName.split("\\."));
             Path targetDir = Paths.get(String.format("%s/%s", outputDirectory, javaDir));
 
             LightProto lightProto = new LightProto(proto, fileName, outerClassName, useOuterClass, generateTextFormat, generateJson);
@@ -94,7 +93,7 @@ public static List<File> generate(List<ProtoFileDescriptor> descriptors, File ou
                 JavaClassSource codecClass = (JavaClassSource) Roaster.parse(is);
                 codecClass.setPackage(javaPackage);
 
-                String javaDir = Joiner.on('/').join(javaPackage.split("\\."));
+                String javaDir = String.join("/", javaPackage.split("\\."));
                 Path codecFile = Paths.get(String.format("%s/%s/LightProtoCodec.java", outputDirectory, javaDir));
                 try (Writer w = Files.newBufferedWriter(codecFile)) {
                     w.write(String.format(
diff --git a/code-generator/src/main/java/io/streamnative/lightproto/generator/LightProtoNumberField.java b/code-generator/src/main/java/io/streamnative/lightproto/generator/LightProtoNumberField.java
index b0242dc..da164db 100644
--- a/code-generator/src/main/java/io/streamnative/lightproto/generator/LightProtoNumberField.java
+++ b/code-generator/src/main/java/io/streamnative/lightproto/generator/LightProtoNumberField.java
@@ -15,9 +15,8 @@
  */
 package io.streamnative.lightproto.generator;
 
-import com.google.common.collect.Maps;
-
 import java.io.PrintWriter;
+import java.util.HashMap;
 import java.util.Map;
 
 import static io.streamnative.lightproto.generator.Util.camelCase;
@@ -25,7 +24,7 @@
 public class LightProtoNumberField extends LightProtoField {
 
 
-    private static final Map<String, String> typeToTag = Maps.newHashMap();
+    private static final Map<String, String> typeToTag = new HashMap<>();
 
     static {
         typeToTag.put("double", "LightProtoCodec.WIRETYPE_FIXED64");
diff --git a/code-generator/src/main/java/io/streamnative/lightproto/generator/Util.java b/code-generator/src/main/java/io/streamnative/lightproto/generator/Util.java
index 1c407cf..ff7b453 100644
--- a/code-generator/src/main/java/io/streamnative/lightproto/generator/Util.java
+++ b/code-generator/src/main/java/io/streamnative/lightproto/generator/Util.java
@@ -17,9 +17,6 @@
 
 import java.io.PrintWriter;
 
-import static com.google.common.base.CaseFormat.LOWER_CAMEL;
-import static com.google.common.base.CaseFormat.LOWER_UNDERSCORE;
-
 public class Util {
 
     public static String camelCase(String... parts) {
@@ -30,7 +27,7 @@ public static String camelCase(String... parts) {
                 continue;
             }
             if (s.contains("_")) {
-                s = LOWER_UNDERSCORE.to(LOWER_CAMEL, s);
+                s = lowerUnderscoreToLowerCamel(s);
             }
 
             if (i != 0) {
@@ -52,7 +49,7 @@ public static String camelCaseFirstUpper(String... parts) {
     public static String upperCase(String... parts) {
         StringBuilder sb = new StringBuilder();
         for (int i = 0; i < parts.length; i++) {
-            String s = LOWER_CAMEL.to(LOWER_UNDERSCORE, parts[i]);
+            String s = lowerCamelToLowerUnderscore(parts[i]);
             if (i != 0) {
                 sb.append('_');
             }
@@ -63,6 +60,48 @@ public static String upperCase(String... parts) {
         return sb.toString().toUpperCase();
     }
 
+    // Mirrors Guava's CaseFormat.LOWER_UNDERSCORE.to(LOWER_CAMEL, s):
+    // splits on '_', lowercases everything, capitalizes the first char of
+    // each non-leading segment.
+    static String lowerUnderscoreToLowerCamel(String s) {
+        if (s.indexOf('_') < 0) {
+            return s;
+        }
+        StringBuilder sb = new StringBuilder(s.length());
+        boolean upperNext = false;
+        for (int i = 0; i < s.length(); i++) {
+            char c = s.charAt(i);
+            if (c == '_') {
+                upperNext = true;
+            } else if (upperNext) {
+                sb.append(Character.toUpperCase(c));
+                upperNext = false;
+            } else {
+                sb.append(Character.toLowerCase(c));
+            }
+        }
+        return sb.toString();
+    }
+
+    // Mirrors Guava's CaseFormat.LOWER_CAMEL.to(LOWER_UNDERSCORE, s):
+    // inserts '_' before every uppercase letter (except a leading one) and
+    // lowercases all letters.
+    static String lowerCamelToLowerUnderscore(String s) {
+        StringBuilder sb = new StringBuilder(s.length() + 4);
+        for (int i = 0; i < s.length(); i++) {
+            char c = s.charAt(i);
+            if (Character.isUpperCase(c)) {
+                if (i > 0) {
+                    sb.append('_');
+                }
+                sb.append(Character.toLowerCase(c));
+            } else {
+                sb.append(c);
+            }
+        }
+        return sb.toString();
+    }
+
     // pluralize/singular rules vendored from JiBX NameUtilities
     // (Copyright (c) 2008-2010, Dennis M. Sosnoski, BSD 3-clause license).
     public static String plural(String name) {
diff --git a/code-generator/src/test/java/io/streamnative/lightproto/generator/UtilTest.java b/code-generator/src/test/java/io/streamnative/lightproto/generator/UtilTest.java
index f63fbaa..7e8b7c7 100644
--- a/code-generator/src/test/java/io/streamnative/lightproto/generator/UtilTest.java
+++ b/code-generator/src/test/java/io/streamnative/lightproto/generator/UtilTest.java
@@ -63,6 +63,55 @@ void pluralizes(String input, String expected) {
         assertEquals(expected, Util.plural(input));
     }
 
+    @ParameterizedTest
+    @CsvSource({
+            // typical snake_case
+            "first_name, firstName",
+            "user_id, userId",
+            "foo_bar_baz, fooBarBaz",
+            "snake_case_name, snakeCaseName",
+            // no underscore: returned as-is (does NOT lowercase)
+            "foo, foo",
+            "MyService, MyService",
+            // numerics
+            "abc_123, abc123",
+            // double underscore
+            "foo__bar, fooBar",
+            // leading underscore capitalizes the next char
+            "_leading, Leading",
+            "_msgSize, Msgsize",
+            // trailing underscore is dropped
+            "trailing_, trailing",
+            // embedded uppercase is normalized to lowercase (matches Guava)
+            "ALL_CAPS, allCaps",
+            "Foo_Bar, fooBar",
+            "FOO_BAR_BAZ, fooBarBaz",
+    })
+    void snakeToCamel(String input, String expected) {
+        assertEquals(expected, Util.lowerUnderscoreToLowerCamel(input));
+    }
+
+    @ParameterizedTest
+    @CsvSource({
+            // typical camelCase
+            "fooBar, foo_bar",
+            "fooBarBaz, foo_bar_baz",
+            "myService, my_service",
+            // leading uppercase: lowercased without leading underscore
+            "MyService, my_service",
+            "X, x",
+            // no uppercase: unchanged
+            "foo, foo",
+            "first_name, first_name",
+            // numerics
+            "abc123, abc123",
+            // already snake-ish stays put
+            "foo_bar_baz, foo_bar_baz",
+    })
+    void camelToSnake(String input, String expected) {
+        assertEquals(expected, Util.lowerCamelToLowerUnderscore(input));
+    }
+
     @ParameterizedTest
     @CsvSource({
             // ends with 'ies': replace with 'y'
diff --git a/pom.xml b/pom.xml
index ce61a10..10f5ad6 100644
--- a/pom.xml
+++ b/pom.xml
@@ -66,7 +66,6 @@
 
         <slf4j.version>1.7.25</slf4j.version>
         <junit.version>5.7.0</junit.version>
-        <guava.version>32.0.0-jre</guava.version>
         <netty.version>4.1.131.Final</netty.version>
         <roaster.version>2.22.2.Final</roaster.version>
         <grpc.version>1.68.0</grpc.version>
@@ -158,11 +157,6 @@
                 <artifactId>slf4j-api</artifactId>
                 <version>${slf4j.version}</version>
             </dependency>
-            <dependency>
-                <groupId>com.google.guava</groupId>
-                <artifactId>guava</artifactId>
-                <version>${guava.version}</version>
-            </dependency>
             <dependency>
                 <groupId>io.netty</groupId>
                 <artifactId>netty-bom</artifactId>