diff --git a/core/src/main/java/org/luaj/vm2/libs/CjsonLib$Encoder.class b/core/src/main/java/org/luaj/vm2/libs/CjsonLib$Encoder.class
new file mode 100644
index 00000000..398816b4
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diff --git a/core/src/main/java/org/luaj/vm2/libs/CjsonLib$Parser.class b/core/src/main/java/org/luaj/vm2/libs/CjsonLib$Parser.class
new file mode 100644
index 00000000..178d0b6c
Binary files /dev/null and b/core/src/main/java/org/luaj/vm2/libs/CjsonLib$Parser.class differ
diff --git a/core/src/main/java/org/luaj/vm2/libs/CjsonLib$decode.class b/core/src/main/java/org/luaj/vm2/libs/CjsonLib$decode.class
new file mode 100644
index 00000000..0612bb6c
Binary files /dev/null and b/core/src/main/java/org/luaj/vm2/libs/CjsonLib$decode.class differ
diff --git a/core/src/main/java/org/luaj/vm2/libs/CjsonLib$encode.class b/core/src/main/java/org/luaj/vm2/libs/CjsonLib$encode.class
new file mode 100644
index 00000000..f0d8d7ea
Binary files /dev/null and b/core/src/main/java/org/luaj/vm2/libs/CjsonLib$encode.class differ
diff --git a/core/src/main/java/org/luaj/vm2/libs/CjsonLib$loader.class b/core/src/main/java/org/luaj/vm2/libs/CjsonLib$loader.class
new file mode 100644
index 00000000..4eb9a291
Binary files /dev/null and b/core/src/main/java/org/luaj/vm2/libs/CjsonLib$loader.class differ
diff --git a/core/src/main/java/org/luaj/vm2/libs/CjsonLib.class b/core/src/main/java/org/luaj/vm2/libs/CjsonLib.class
new file mode 100644
index 00000000..67aeaf83
Binary files /dev/null and b/core/src/main/java/org/luaj/vm2/libs/CjsonLib.class differ
diff --git a/core/src/main/java/org/luaj/vm2/libs/CjsonLib.java b/core/src/main/java/org/luaj/vm2/libs/CjsonLib.java
new file mode 100644
index 00000000..4c77468b
--- /dev/null
+++ b/core/src/main/java/org/luaj/vm2/libs/CjsonLib.java
@@ -0,0 +1,414 @@
+package org.luaj.vm2.libs;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import org.luaj.vm2.LuaDouble;
+import org.luaj.vm2.LuaInteger;
+import org.luaj.vm2.LuaString;
+import org.luaj.vm2.LuaTable;
+import org.luaj.vm2.LuaUserdata;
+import org.luaj.vm2.LuaValue;
+import org.luaj.vm2.Varargs;
+
+/**
+ * Minimal built-in cjson-compatible module implemented in Java.
+ * It supports require("cjson"), cjson.encode(...), cjson.decode(...), and cjson.null.
+ */
+public class CjsonLib extends TwoArgFunction {
+
+	private static final Object NULL_SENTINEL = new Object();
+
+	public LuaValue call(LuaValue modname, LuaValue env) {
+		LuaValue pkg = env.get("package");
+		if (!pkg.istable()) {
+			return env;
+		}
+		LuaValue preload = pkg.get("preload");
+		if (!preload.istable()) {
+			return env;
+		}
+		preload.set("cjson", new loader());
+		return env;
+	}
+
+	static LuaValue nullValue() {
+		return new LuaUserdata(NULL_SENTINEL);
+	}
+
+	static boolean isNullSentinel(LuaValue value) {
+		return value.isuserdata() && value.touserdata() == NULL_SENTINEL;
+	}
+
+	static final class loader extends TwoArgFunction {
+		public LuaValue call(LuaValue modname, LuaValue env) {
+			LuaTable module = new LuaTable(0, 3);
+			module.set("encode", new encode());
+			module.set("decode", new decode());
+			module.set("null", nullValue());
+			return module;
+		}
+	}
+
+	static final class encode extends OneArgFunction {
+		public LuaValue call(LuaValue value) {
+			StringBuilder out = new StringBuilder();
+			new Encoder().append(value, out, new HashSet());
+			return LuaValue.valueOf(out.toString());
+		}
+	}
+
+	static final class decode extends OneArgFunction {
+		public LuaValue call(LuaValue value) {
+			Parser parser = new Parser(value.checkjstring());
+			LuaValue result = parser.parseValue();
+			parser.skipWhitespace();
+			if (!parser.eof()) {
+				error("trailing garbage");
+			}
+			return result;
+		}
+	}
+
+	private static final class Encoder {
+		void append(LuaValue value, StringBuilder out, Set seen) {
+			if (value.isnil() || isNullSentinel(value)) {
+				out.append("null");
+			} else if (value.isboolean()) {
+				out.append(value.toboolean() ? "true" : "false");
+			} else if (value.isnumber()) {
+				double d = value.todouble();
+				if (Double.isNaN(d) || Double.isInfinite(d)) {
+					error("cannot encode NaN or infinite numbers");
+				}
+				out.append(value.tojstring());
+			} else if (value.isstring()) {
+				appendString(value.checkjstring(), out);
+			} else if (value.istable()) {
+				appendTable(value.checktable(), out, seen);
+			} else {
+				error("unsupported type for json encoding: " + value.typename());
+			}
+		}
+
+		private void appendTable(LuaTable table, StringBuilder out, Set seen) {
+			if (!seen.add(table)) {
+				error("circular reference");
+			}
+			try {
+				if (isArray(table)) {
+					out.append('[');
+					int n = table.length();
+					for (int i = 1; i <= n; i++) {
+						if (i > 1) {
+							out.append(',');
+						}
+						append(table.get(i), out, seen);
+					}
+					out.append(']');
+				} else {
+					out.append('{');
+					LuaValue key = LuaValue.NIL;
+					boolean first = true;
+					while (true) {
+						Varargs next = table.next(key);
+						key = next.arg1();
+						if (key.isnil()) {
+							break;
+						}
+						if (!first) {
+							out.append(',');
+						}
+						first = false;
+						appendString(key.checkjstring(), out);
+						out.append(':');
+						append(next.arg(2), out, seen);
+					}
+					out.append('}');
+				}
+			} finally {
+				seen.remove(table);
+			}
+		}
+
+		private boolean isArray(LuaTable table) {
+			int n = table.length();
+			int count = 0;
+			LuaValue key = LuaValue.NIL;
+			while (true) {
+				Varargs next = table.next(key);
+				key = next.arg1();
+				if (key.isnil()) {
+					break;
+				}
+				if (!key.isinttype()) {
+					return false;
+				}
+				int index = key.toint();
+				if (index < 1 || index > n) {
+					return false;
+				}
+				count++;
+			}
+			return count == n;
+		}
+
+		private void appendString(String value, StringBuilder out) {
+			out.append('"');
+			for (int i = 0; i < value.length(); i++) {
+				char c = value.charAt(i);
+				switch (c) {
+				case '"':
+				case '\\':
+					out.append('\\').append(c);
+					break;
+				case '\b':
+					out.append("\\b");
+					break;
+				case '\f':
+					out.append("\\f");
+					break;
+				case '\n':
+					out.append("\\n");
+					break;
+				case '\r':
+					out.append("\\r");
+					break;
+				case '\t':
+					out.append("\\t");
+					break;
+				default:
+					if (c < 0x20) {
+						String hex = Integer.toHexString(c);
+						out.append("\\u");
+						for (int j = hex.length(); j < 4; j++) {
+							out.append('0');
+						}
+						out.append(hex);
+					} else {
+						out.append(c);
+					}
+				}
+			}
+			out.append('"');
+		}
+	}
+
+	private static final class Parser {
+		private final String input;
+		private int pos;
+
+		Parser(String input) {
+			this.input = input;
+		}
+
+		LuaValue parseValue() {
+			skipWhitespace();
+			if (eof()) {
+				error("unexpected end of json");
+			}
+			char c = input.charAt(pos);
+			switch (c) {
+			case '{':
+				return parseObject();
+			case '[':
+				return parseArray();
+			case '"':
+				return LuaValue.valueOf(parseString());
+			case 't':
+				expect("true");
+				return LuaValue.TRUE;
+			case 'f':
+				expect("false");
+				return LuaValue.FALSE;
+			case 'n':
+				expect("null");
+				return nullValue();
+			default:
+				if (c == '-' || (c >= '0' && c <= '9')) {
+					return parseNumber();
+				}
+				error("invalid json value");
+				return LuaValue.NIL;
+			}
+		}
+
+		private LuaValue parseObject() {
+			LuaTable table = new LuaTable();
+			pos++;
+			skipWhitespace();
+			if (consume('}')) {
+				return table;
+			}
+			while (true) {
+				skipWhitespace();
+				if (eof() || input.charAt(pos) != '"') {
+					error("expected string key");
+				}
+				String key = parseString();
+				skipWhitespace();
+				if (!consume(':')) {
+					error("expected ':'");
+				}
+				table.set(key, parseValue());
+				skipWhitespace();
+				if (consume('}')) {
+					return table;
+				}
+				if (!consume(',')) {
+					error("expected ',' or '}'");
+				}
+			}
+		}
+
+		private LuaValue parseArray() {
+			LuaTable table = new LuaTable();
+			int index = 1;
+			pos++;
+			skipWhitespace();
+			if (consume(']')) {
+				return table;
+			}
+			while (true) {
+				table.set(index++, parseValue());
+				skipWhitespace();
+				if (consume(']')) {
+					return table;
+				}
+				if (!consume(',')) {
+					error("expected ',' or ']'");
+				}
+			}
+		}
+
+		private LuaValue parseNumber() {
+			int start = pos;
+			if (input.charAt(pos) == '-') {
+				pos++;
+			}
+			readDigits();
+			boolean isFloat = false;
+			if (!eof() && input.charAt(pos) == '.') {
+				isFloat = true;
+				pos++;
+				readDigits();
+			}
+			if (!eof()) {
+				char c = input.charAt(pos);
+				if (c == 'e' || c == 'E') {
+					isFloat = true;
+					pos++;
+					if (!eof()) {
+						char sign = input.charAt(pos);
+						if (sign == '+' || sign == '-') {
+							pos++;
+						}
+					}
+					readDigits();
+				}
+			}
+			String number = input.substring(start, pos);
+			try {
+				return isFloat ? LuaValue.valueOf(Double.parseDouble(number)) : LuaValue.valueOf(Long.parseLong(number));
+			} catch (NumberFormatException e) {
+				error("invalid number");
+				return LuaValue.NIL;
+			}
+		}
+
+		private void readDigits() {
+			int start = pos;
+			while (!eof()) {
+				char c = input.charAt(pos);
+				if (c < '0' || c > '9') {
+					break;
+				}
+				pos++;
+			}
+			if (start == pos) {
+				error("invalid number");
+			}
+		}
+
+		private String parseString() {
+			StringBuffer out = new StringBuffer();
+			pos++;
+			while (!eof()) {
+				char c = input.charAt(pos++);
+				if (c == '"') {
+					return out.toString();
+				}
+				if (c != '\\') {
+					out.append(c);
+					continue;
+				}
+				if (eof()) {
+					error("unterminated escape");
+				}
+				char esc = input.charAt(pos++);
+				switch (esc) {
+				case '"':
+				case '\\':
+				case '/':
+					out.append(esc);
+					break;
+				case 'b':
+					out.append('\b');
+					break;
+				case 'f':
+					out.append('\f');
+					break;
+				case 'n':
+					out.append('\n');
+					break;
+				case 'r':
+					out.append('\r');
+					break;
+				case 't':
+					out.append('\t');
+					break;
+				case 'u':
+					if (pos + 4 > input.length()) {
+						error("invalid unicode escape");
+					}
+					out.append((char) Integer.parseInt(input.substring(pos, pos + 4), 16));
+					pos += 4;
+					break;
+				default:
+					error("invalid escape");
+				}
+			}
+			error("unterminated string");
+			return null;
+		}
+
+		void skipWhitespace() {
+			while (!eof()) {
+				char c = input.charAt(pos);
+				if (c != ' ' && c != '\n' && c != '\r' && c != '\t') {
+					break;
+				}
+				pos++;
+			}
+		}
+
+		boolean eof() {
+			return pos >= input.length();
+		}
+
+		private void expect(String token) {
+			if (!input.regionMatches(pos, token, 0, token.length())) {
+				error("expected '" + token + "'");
+			}
+			pos += token.length();
+		}
+
+		private boolean consume(char c) {
+			if (!eof() && input.charAt(pos) == c) {
+				pos++;
+				return true;
+			}
+			return false;
+		}
+	}
+}
diff --git a/jme/src/main/java/org/luaj/vm2/libs/jme/JmePlatform.java b/jme/src/main/java/org/luaj/vm2/libs/jme/JmePlatform.java
index cbe5b160..f796dd1d 100644
--- a/jme/src/main/java/org/luaj/vm2/libs/jme/JmePlatform.java
+++ b/jme/src/main/java/org/luaj/vm2/libs/jme/JmePlatform.java
@@ -95,6 +95,7 @@ public class JmePlatform {
 		Globals globals = new Globals();
 		globals.load(new BaseLib());
 		globals.load(new PackageLib());
+		globals.load(new CjsonLib());
 		globals.load(new Bit32Lib());
 		globals.load(new OsLib());
 		globals.load(new MathLib());
diff --git a/jse/src/main/java/org/luaj/vm2/libs/jse/JsePlatform.class b/jse/src/main/java/org/luaj/vm2/libs/jse/JsePlatform.class
index 1ca36e41..97e6cd33 100644
Binary files a/jse/src/main/java/org/luaj/vm2/libs/jse/JsePlatform.class and b/jse/src/main/java/org/luaj/vm2/libs/jse/JsePlatform.class differ
diff --git a/jse/src/main/java/org/luaj/vm2/libs/jse/JsePlatform.java b/jse/src/main/java/org/luaj/vm2/libs/jse/JsePlatform.java
index 93b84dca..5a2864f5 100644
--- a/jse/src/main/java/org/luaj/vm2/libs/jse/JsePlatform.java
+++ b/jse/src/main/java/org/luaj/vm2/libs/jse/JsePlatform.java
@@ -88,6 +88,7 @@ public class JsePlatform {
 		Globals globals = new Globals();
 		globals.load(new JseBaseLib());
 		globals.load(new PackageLib());
+		globals.load(new CjsonLib());
 		globals.load(new Bit32Lib());
 		globals.load(new TableLib());
 		globals.load(new JseStringLib());
diff --git a/jse/src/test/java/org/luaj/vm2/FragmentsTest.java b/jse/src/test/java/org/luaj/vm2/FragmentsTest.java
index db3455cf..4da8854a 100644
--- a/jse/src/test/java/org/luaj/vm2/FragmentsTest.java
+++ b/jse/src/test/java/org/luaj/vm2/FragmentsTest.java
@@ -390,6 +390,25 @@ public class FragmentsTest extends TestSuite {
 			}
 		}
 
+		public void testCjsonRequireEncodeDecode() {
+			try {
+				Globals globals = JsePlatform.standardGlobals();
+				Varargs result = globals.load(
+					"local cjson = require('cjson')\n" +
+					"local json = cjson.encode({name='lua', values={1, true, cjson.null}})\n" +
+					"local decoded = cjson.decode(json)\n" +
+					"return decoded.name, decoded.values[1], decoded.values[2], decoded.values[3] == cjson.null\n",
+					"cjson.lua").invoke();
+				assertEquals(LuaValue.valueOf("lua"), result.arg1());
+				assertEquals(LuaValue.valueOf(1), result.arg(2));
+				assertEquals(LuaValue.TRUE, result.arg(3));
+				assertEquals(LuaValue.TRUE, result.arg(4));
+			} catch (Exception e) {
+				e.printStackTrace();
+				fail(e.toString());
+			}
+		}
+
 		public void testTableMove() {
 			runFragment(
 				LuaValue.varargsOf(new LuaValue[] {