diff --git a/src/main/java/net/logicsquad/pal/Code.java b/src/main/java/net/logicsquad/pal/Code.java
index 55524c7..2df3332 100644
--- a/src/main/java/net/logicsquad/pal/Code.java
+++ b/src/main/java/net/logicsquad/pal/Code.java
@@ -12,7 +12,7 @@ public class Code {
 	 * 
 	 * @see Mnemonic
 	 */
-	private String mnemonic;
+	private Mnemonic mnemonic;
 
 	/** The first argument to the instruction. */
 	private int first;
@@ -45,7 +45,7 @@ public class Code {
 	 *            originated.
 	 */
 	public Code(String mnemonic, int first, Object second, int lineno) {
-		this.mnemonic = mnemonic;
+		this.mnemonic = Mnemonic.valueOf(mnemonic);
 		this.first = first;
 		this.second = second;
 		this.lineno = lineno;
@@ -58,7 +58,7 @@ public Code(String mnemonic, int first, Object second, int lineno) {
 	 * @return A <code>String</code> containing the three letter mnemonic for
 	 *         this instruction.
 	 */
-	public String getMnemonic() {
+	public Mnemonic getMnemonic() {
 		return mnemonic;
 	}
 
diff --git a/src/main/java/net/logicsquad/pal/Mnemonic.java b/src/main/java/net/logicsquad/pal/Mnemonic.java
index c1e8ec3..b39313d 100644
--- a/src/main/java/net/logicsquad/pal/Mnemonic.java
+++ b/src/main/java/net/logicsquad/pal/Mnemonic.java
@@ -1,87 +1,104 @@
 package net.logicsquad.pal;
 
-import java.util.Arrays;
-
 /**
- * A class to define constant ints to represent mnemonics, and to provide
- * conversion methods between <code>int</code> and <code>String</code>
- * representations.
+ * Represents the set of instruction mnemonics.
  * 
  * @author Philip Roberts &lt;philip.roberts@gmail.com&gt;
  * @author Paul Hoadley &lt;paulh@logicsquad.net&gt;
  */
-public class Mnemonic {
-	/**
-	 * A lexicographically ordered array of the available mnemonics.
-	 */
-	private static final String[] mnemonicList = { "CAL", "INC", "JIF", "JMP",
-			"LCI", "LCR", "LCS", "LDA", "LDI", "LDU", "LDV", "MST", "OPR",
-			"RDI", "RDR", "REH", "SIG", "STI", "STO" };
-
-	// Important: The following constants must correspond to their
-	// index in the "mnemonicList" array.
-
-	/** Constant to represent the <code>CAL</code> mnemonic. */
-	public static final int CAL = 0;
-	/** Constant to represent the <code>INC</code> mnemonic. */
-	public static final int INC = 1;
-	/** Constant to represent the <code>JIF</code> mnemonic. */
-	public static final int JIF = 2;
-	/** Constant to represent the <code>JMP</code> mnemonic. */
-	public static final int JMP = 3;
-	/** Constant to represent the <code>LCI</code> mnemonic. */
-	public static final int LCI = 4;
-	/** Constant to represent the <code>LCR</code> mnemonic. */
-	public static final int LCR = 5;
-	/** Constant to represent the <code>LCS</code> mnemonic. */
-	public static final int LCS = 6;
-	/** Constant to represent the <code>LDA</code> mnemonic. */
-	public static final int LDA = 7;
-	/** Constant to represent the <code>LDI</code> mnemonic. */
-	public static final int LDI = 8;
-	/** Constant to represent the <code>LDU</code> mnemonic. */
-	public static final int LDU = 9;
-	/** Constant to represent the <code>LDV</code> mnemonic. */
-	public static final int LDV = 10;
-	/** Constant to represent the <code>MST</code> mnemonic. */
-	public static final int MST = 11;
-	/** Constant to represent the <code>OPR</code> mnemonic. */
-	public static final int OPR = 12;
-	/** Constant to represent the <code>RDI</code> mnemonic. */
-	public static final int RDI = 13;
-	/** Constant to represent the <code>RDR</code> mnemonic. */
-	public static final int RDR = 14;
-	/** Constant to represent the <code>REH</code> mnemonic. */
-	public static final int REH = 15;
-	/** Constant to represent the <code>SIG</code> mnemonic. */
-	public static final int SIG = 16;
-	/** Constant to represent the <code>STI</code> mnemonic. */
-	public static final int STI = 17;
-	/** Constant to represent the <code>STO</code> mnemonic. */
-	public static final int STO = 18;
-
-	/**
-	 * Returns the <code>int</code> representing the supplied mnemonic.
-	 * 
-	 * @param m
-	 *            A <code>String</code> containing the mnemonic.
-	 * @return An <code>int</code> representing the supplied mnemonic.
-	 */
-	public static int mnemonicToInt(String m) {
-		return Arrays.binarySearch(mnemonicList, m);
-	}
-
-	/**
-	 * Returns the <code>String</code> corresponding to the supplied
-	 * <code>int</code> code.
-	 * 
-	 * @param i
-	 *            An <code>int</code> representing a mnemonic.
-	 * @return The corresponding mnemonic.
-	 */
-	public static String intToMnemonic(int i) {
-		if (i < mnemonicList.length && i >= 0)
-			return mnemonicList[i];
-		return "XXX";
-	}
+public enum Mnemonic {
+	/**
+	 * <code>CAL</code>
+	 */
+	CAL,
+
+	/**
+	 * <code>INC</code>
+	 */
+	INC,
+
+	/**
+	 * <code>JIF</code>
+	 */
+	JIF,
+
+	/**
+	 * <code>JMP</code>
+	 */
+	JMP,
+
+	/**
+	 * <code>LCI</code>
+	 */
+	LCI,
+
+	/**
+	 * <code>LCR</code>
+	 */
+	LCR,
+
+	/**
+	 * <code>LCS</code>
+	 */
+	LCS,
+
+	/**
+	 * <code>LDA</code>
+	 */
+	LDA,
+
+	/**
+	 * <code>LDI</code>
+	 */
+	LDI,
+
+	/**
+	 * <code>LDU</code>
+	 */
+	LDU,
+
+	/**
+	 * <code>LDV</code>
+	 */
+	LDV,
+
+	/**
+	 * <code>MST</code>
+	 */
+	MST,
+
+	/**
+	 * <code>OPR</code>
+	 */
+	OPR,
+
+	/**
+	 * <code>RDI</code>
+	 */
+	RDI,
+
+	/**
+	 * <code>RDR</code>
+	 */
+	RDR,
+
+	/**
+	 * <code>REH</code>
+	 */
+	REH,
+
+	/**
+	 * <code>SIG</code>
+	 */
+	SIG,
+
+	/**
+	 * <code>STI</code>
+	 */
+	STI,
+
+	/**
+	 * <code>STO</code>
+	 */
+	STO;
 }
diff --git a/src/main/java/net/logicsquad/pal/PAL.java b/src/main/java/net/logicsquad/pal/PAL.java
index fc3bb98..d76c2fc 100644
--- a/src/main/java/net/logicsquad/pal/PAL.java
+++ b/src/main/java/net/logicsquad/pal/PAL.java
@@ -212,7 +212,7 @@ ExitStatus execute() {
 
 			Data tos, ntos, returnPoint, loadedVal;
 
-			switch (Mnemonic.mnemonicToInt(currInst.getMnemonic())) {
+			switch (currInst.getMnemonic()) {
 			case Mnemonic.CAL:
 				// Procedure/function call.