diff --git a/src/validator.ts b/src/validator.ts
index 7c55e83..9321cec 100644
--- a/src/validator.ts
+++ b/src/validator.ts
@@ -30,7 +30,6 @@ function isValidIdentifier(name: string): boolean {
   return !/[\s;()[\]{}='"#@.]/.test(name)
 }
 
-// Opcodes that require operands
 const OPCODES_WITH_OPERANDS = new Set([
   OpCode.PUSH,
   OpCode.LOAD,
@@ -46,7 +45,6 @@ const OPCODES_WITH_OPERANDS = new Set([
   OpCode.CALL_NATIVE,
 ])
 
-// Opcodes that should NOT have operands
 const OPCODES_WITHOUT_OPERANDS = new Set([
   OpCode.POP,
   OpCode.DUP,
@@ -78,6 +76,21 @@ const OPCODES_WITHOUT_OPERANDS = new Set([
   OpCode.DICT_HAS,
 ])
 
+// immediate = immediate number, eg #5
+const OPCODES_REQUIRING_IMMEDIATE_OR_LABEL = new Set([
+  OpCode.JUMP,
+  OpCode.JUMP_IF_FALSE,
+  OpCode.JUMP_IF_TRUE,
+  OpCode.PUSH_TRY,
+  OpCode.PUSH_FINALLY,
+])
+
+// immediate = immediate number, eg #5
+const OPCODES_REQUIRING_IMMEDIATE = new Set([
+  OpCode.MAKE_ARRAY,
+  OpCode.MAKE_DICT,
+])
+
 export function validateBytecode(source: string): ValidationResult {
   const errors: ValidationError[] = []
   const lines = source.split("\n")
@@ -172,6 +185,26 @@ export function validateBytecode(source: string): ValidationResult {
 
     // Validate specific operand formats
     if (operand) {
+      if (OPCODES_REQUIRING_IMMEDIATE_OR_LABEL.has(opCode)) {
+        if (!operand.startsWith('#') && !operand.startsWith('.')) {
+          errors.push({
+            line: lineNum,
+            message: `${opName} requires immediate (#number) or label (.label), got: ${operand}`,
+          })
+          continue
+        }
+      }
+
+      if (OPCODES_REQUIRING_IMMEDIATE.has(opCode)) {
+        if (!operand.startsWith('#')) {
+          errors.push({
+            line: lineNum,
+            message: `${opName} requires immediate number (#count), got: ${operand}`,
+          })
+          continue
+        }
+      }
+
       // Check for label references
       if (operand.startsWith('.') && !operand.includes('(')) {
         const labelName = operand.slice(1)
@@ -246,7 +279,7 @@ export function validateBytecode(source: string): ValidationResult {
               }
             } else if (param.includes('=')) {
               // Default parameter
-              const [name, defaultValue] = param.split('=')
+              const [name] = param.split('=')
               if (!isValidIdentifier(name!.trim())) {
                 errors.push({
                   line: lineNum,
diff --git a/tests/validator.test.ts b/tests/validator.test.ts
index 8588e78..0afd65b 100644
--- a/tests/validator.test.ts
+++ b/tests/validator.test.ts
@@ -200,3 +200,113 @@ test("formatValidationErrors produces readable output", () => {
   expect(formatted).toContain("Line")
   expect(formatted).toContain("UNKNOWN")
 })
+
+test("detects JUMP without # or .label", () => {
+  const source = `
+    JUMP 5
+    HALT
+  `
+  const result = validateBytecode(source)
+  expect(result.valid).toBe(false)
+  expect(result.errors[0]!.message).toContain("JUMP requires immediate (#number) or label (.label)")
+})
+
+test("detects JUMP_IF_TRUE without # or .label", () => {
+  const source = `
+    PUSH true
+    JUMP_IF_TRUE 2
+    HALT
+  `
+  const result = validateBytecode(source)
+  expect(result.valid).toBe(false)
+  expect(result.errors[0]!.message).toContain("JUMP_IF_TRUE requires immediate (#number) or label (.label)")
+})
+
+test("detects JUMP_IF_FALSE without # or .label", () => {
+  const source = `
+    PUSH false
+    JUMP_IF_FALSE 2
+    HALT
+  `
+  const result = validateBytecode(source)
+  expect(result.valid).toBe(false)
+  expect(result.errors[0]!.message).toContain("JUMP_IF_FALSE requires immediate (#number) or label (.label)")
+})
+
+test("allows JUMP with immediate number", () => {
+  const source = `
+    JUMP #2
+    PUSH 999
+    HALT
+  `
+  const result = validateBytecode(source)
+  expect(result.valid).toBe(true)
+})
+
+test("detects MAKE_ARRAY without #", () => {
+  const source = `
+    PUSH 1
+    PUSH 2
+    MAKE_ARRAY 2
+    HALT
+  `
+  const result = validateBytecode(source)
+  expect(result.valid).toBe(false)
+  expect(result.errors[0]!.message).toContain("MAKE_ARRAY requires immediate number (#count)")
+})
+
+test("detects MAKE_DICT without #", () => {
+  const source = `
+    PUSH "key"
+    PUSH "value"
+    MAKE_DICT 1
+    HALT
+  `
+  const result = validateBytecode(source)
+  expect(result.valid).toBe(false)
+  expect(result.errors[0]!.message).toContain("MAKE_DICT requires immediate number (#count)")
+})
+
+test("allows MAKE_ARRAY with immediate number", () => {
+  const source = `
+    PUSH 1
+    PUSH 2
+    MAKE_ARRAY #2
+    HALT
+  `
+  const result = validateBytecode(source)
+  expect(result.valid).toBe(true)
+})
+
+test("detects PUSH_TRY without # or .label", () => {
+  const source = `
+    PUSH_TRY 5
+    HALT
+  `
+  const result = validateBytecode(source)
+  expect(result.valid).toBe(false)
+  expect(result.errors[0]!.message).toContain("PUSH_TRY requires immediate (#number) or label (.label)")
+})
+
+test("detects PUSH_FINALLY without # or .label", () => {
+  const source = `
+    PUSH_FINALLY 5
+    HALT
+  `
+  const result = validateBytecode(source)
+  expect(result.valid).toBe(false)
+  expect(result.errors[0]!.message).toContain("PUSH_FINALLY requires immediate (#number) or label (.label)")
+})
+
+test("allows PUSH_TRY with label", () => {
+  const source = `
+    PUSH_TRY .catch
+    PUSH 42
+    HALT
+    .catch:
+    PUSH null
+    HALT
+  `
+  const result = validateBytecode(source)
+  expect(result.valid).toBe(true)
+})