diff --git a/src/core/operations/DisassembleX86.mjs b/src/core/operations/DisassembleX86.mjs
index bdaf348aa1..1705967f41 100644
--- a/src/core/operations/DisassembleX86.mjs
+++ b/src/core/operations/DisassembleX86.mjs
@@ -8,6 +8,34 @@ import Operation from "../Operation.mjs";
 import * as disassemble from "../vendor/DisassembleX86-64.mjs";
 import OperationError from "../errors/OperationError.mjs";
 
+/**
+ * Parses a hexadecimal address value used by the disassembler.
+ *
+ * The underlying disassembler interprets both the code segment and the offset as
+ * hexadecimal, and renders them back as hexadecimal, so these arguments accept the
+ * common ways of writing a hex literal: bare (`ABC`), prefixed (`0xABC`) or suffixed
+ * (`ABCh`).
+ *
+ * @param {string} value
+ * @param {string} name - Argument name, used in the error message.
+ * @param {number} [padTo=0] - Left-pad the result with zeroes to this many digits.
+ * @returns {string} The bare hex digits, ready to be passed to SetBasePosition.
+ *
+ * @throws {OperationError} if the value is not a valid hexadecimal number.
+ */
+function parseHexAddress(value, name, padTo = 0) {
+    const trimmed = value.toString().trim();
+    const hex = trimmed.replace(/^0x/i, "").replace(/h$/i, "");
+
+    if (hex === "" || !/^[\da-f]+$/i.test(hex)) {
+        throw new OperationError(`Invalid ${name}: '${trimmed}' is not a hexadecimal number.`);
+    }
+
+    // SetBasePosition reads the code segment from the last four characters it is given,
+    // so shorter values must be padded to avoid losing their leading digits.
+    return hex.padStart(padTo, "0");
+}
+
 /**
  * Disassemble x86 operation
  */
@@ -46,13 +74,15 @@ class DisassembleX86 extends Operation {
             },
             {
                 "name": "Code Segment (CS)",
-                "type": "number",
-                "value": 16
+                "type": "string",
+                "value": "16",
+                "hint": "Hexadecimal, e.g. 16, 0xABC or ABCh"
             },
             {
                 "name": "Offset (IP)",
-                "type": "number",
-                "value": 0
+                "type": "string",
+                "value": "0",
+                "hint": "Hexadecimal, e.g. 0, 0x1000 or 1000h"
             },
             {
                 "name": "Show instruction hex",
@@ -122,7 +152,10 @@ class DisassembleX86 extends Operation {
                 break;
         }
 
-        disassemble.SetBasePosition(codeSegment + ":" + offset);
+        disassemble.SetBasePosition(
+            parseHexAddress(codeSegment, "Code Segment (CS)", 4) + ":" +
+            parseHexAddress(offset, "Offset (IP)")
+        );
         disassemble.setShowInstructionHex(showInstructionHex);
         disassemble.setShowInstructionPos(showInstructionPos);
         disassemble.LoadBinCode(input.replace(/\s/g, ""));
diff --git a/tests/operations/tests/DisassembleX86.mjs b/tests/operations/tests/DisassembleX86.mjs
new file mode 100644
index 0000000000..08414fa7de
--- /dev/null
+++ b/tests/operations/tests/DisassembleX86.mjs
@@ -0,0 +1,89 @@
+/**
+ * Disassemble x86 tests.
+ *
+ * @author arjun2075
+ *
+ * @copyright Crown Copyright 2026
+ * @license Apache-2.0
+ */
+import TestRegister from "../../lib/TestRegister.mjs";
+
+TestRegister.addTests([
+    {
+        name: "Disassemble x86: default code segment is unchanged",
+        input: "90",
+        expectedMatch: /0016:0000\s+NOP/,
+        recipeConfig: [
+            {
+                op: "Disassemble x86",
+                args: ["16", "Full x86 architecture", "16", "0", false, true],
+            },
+        ],
+    },
+    {
+        name: "Disassemble x86: hex code segment with 0x prefix",
+        input: "90",
+        expectedMatch: /0ABC:0000\s+NOP/,
+        recipeConfig: [
+            {
+                op: "Disassemble x86",
+                args: ["16", "Full x86 architecture", "0xABC", "0", false, true],
+            },
+        ],
+    },
+    {
+        name: "Disassemble x86: hex code segment with h suffix",
+        input: "90",
+        expectedMatch: /0ABC:0000\s+NOP/,
+        recipeConfig: [
+            {
+                op: "Disassemble x86",
+                args: ["16", "Full x86 architecture", "ABCh", "0", false, true],
+            },
+        ],
+    },
+    {
+        name: "Disassemble x86: bare hex code segment",
+        input: "90",
+        expectedMatch: /0ABC:0000\s+NOP/,
+        recipeConfig: [
+            {
+                op: "Disassemble x86",
+                args: ["16", "Full x86 architecture", "ABC", "0", false, true],
+            },
+        ],
+    },
+    {
+        name: "Disassemble x86: hex offset with 0x prefix",
+        input: "90",
+        expectedMatch: /0016:1000\s+NOP/,
+        recipeConfig: [
+            {
+                op: "Disassemble x86",
+                args: ["16", "Full x86 architecture", "16", "0x1000", false, true],
+            },
+        ],
+    },
+    {
+        name: "Disassemble x86: invalid code segment is rejected",
+        input: "90",
+        expectedOutput: "Invalid Code Segment (CS): 'wibble' is not a hexadecimal number.",
+        recipeConfig: [
+            {
+                op: "Disassemble x86",
+                args: ["16", "Full x86 architecture", "wibble", "0", false, true],
+            },
+        ],
+    },
+    {
+        name: "Disassemble x86: invalid offset is rejected",
+        input: "90",
+        expectedOutput: "Invalid Offset (IP): 'wibble' is not a hexadecimal number.",
+        recipeConfig: [
+            {
+                op: "Disassemble x86",
+                args: ["16", "Full x86 architecture", "16", "wibble", false, true],
+            },
+        ],
+    },
+]);