diff --git a/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodeLinkPrecheckService.java b/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodeLinkPrecheckService.java
index 6caaab7a..83d336c0 100644
--- a/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodeLinkPrecheckService.java
+++ b/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodeLinkPrecheckService.java
@@ -54,7 +54,7 @@ public class BytecodeLinkPrecheckService {
                         "truncated opcode at pc=" + pc);
             }
             final var opcode = readU16(module.code(), pc);
-            final var size = sizeForOpcode(opcode);
+            final var size = sizeForOpcode(opcode, pc);
             if (pc + size > module.code().length) {
                 throw new BytecodeMarshalingException(
                         BytecodeMarshalingErrorCode.MARSHAL_VERIFY_PRECHECK_TRUNCATED_INSTRUCTION,
@@ -72,13 +72,16 @@ public class BytecodeLinkPrecheckService {
         }
     }
 
-    private int sizeForOpcode(final int opcode) {
-        return switch (opcode) {
-            case 0x50, 0x71, 0x72, 0x02, 0x03, 0x04, 0x10, 0x18, 0x40, 0x41, 0x42, 0x43, 0x56 -> 6;
-            case 0x14, 0x15, 0x52, 0x54 -> 10;
-            case 0x16 -> 3;
-            default -> 2;
-        };
+    private int sizeForOpcode(
+            final int opcode,
+            final int pc) {
+        try {
+            return BytecodeOpcodeLayout.sizeForOpcode(opcode);
+        } catch (BytecodeMarshalingException ignored) {
+            throw new BytecodeMarshalingException(
+                    BytecodeMarshalingErrorCode.MARSHAL_VERIFY_PRECHECK_UNKNOWN_OPCODE,
+                    "unknown opcode 0x%04X at pc=%d".formatted(opcode, pc));
+        }
     }
 
     private int readU16(final byte[] code, final int offset) {
diff --git a/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodeMarshalingErrorCode.java b/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodeMarshalingErrorCode.java
index 7053f2aa..5b155dad 100644
--- a/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodeMarshalingErrorCode.java
+++ b/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodeMarshalingErrorCode.java
@@ -10,6 +10,7 @@ public enum BytecodeMarshalingErrorCode {
     MARSHAL_VERIFY_PRECHECK_FUNCTION_BOUNDS_INVALID,
     MARSHAL_VERIFY_PRECHECK_EXPORT_FUNC_INDEX_INVALID,
     MARSHAL_VERIFY_PRECHECK_HOSTCALL_INDEX_INVALID,
+    MARSHAL_VERIFY_PRECHECK_UNKNOWN_OPCODE,
     MARSHAL_VERIFY_PRECHECK_TRUNCATED_INSTRUCTION,
     MARSHAL_VERIFY_PRECHECK_UNTERMINATED_FUNCTION,
 }
diff --git a/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodeOpcodeLayout.java b/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodeOpcodeLayout.java
new file mode 100644
index 00000000..4cf19b75
--- /dev/null
+++ b/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodeOpcodeLayout.java
@@ -0,0 +1,42 @@
+package p.studio.compiler.backend.bytecode;
+
+import java.util.Map;
+
+final class BytecodeOpcodeLayout {
+    private static final Map<Integer, Integer> SIZE_BY_OPCODE = Map.ofEntries(
+            Map.entry(0x01, 2),
+            Map.entry(0x02, 6),
+            Map.entry(0x03, 6),
+            Map.entry(0x04, 6),
+            Map.entry(0x10, 6),
+            Map.entry(0x14, 10),
+            Map.entry(0x15, 10),
+            Map.entry(0x16, 3),
+            Map.entry(0x17, 6),
+            Map.entry(0x18, 6),
+            Map.entry(0x40, 6),
+            Map.entry(0x41, 6),
+            Map.entry(0x42, 6),
+            Map.entry(0x43, 6),
+            Map.entry(0x50, 6),
+            Map.entry(0x51, 2),
+            Map.entry(0x52, 10),
+            Map.entry(0x54, 10),
+            Map.entry(0x56, 6),
+            Map.entry(0x70, 6),
+            Map.entry(0x71, 6),
+            Map.entry(0x72, 6));
+
+    private BytecodeOpcodeLayout() {
+    }
+
+    static int sizeForOpcode(final int opcode) {
+        final var size = SIZE_BY_OPCODE.get(opcode);
+        if (size == null) {
+            throw new BytecodeMarshalingException(
+                    BytecodeMarshalingErrorCode.MARSHAL_VERIFY_PRECHECK_UNKNOWN_OPCODE,
+                    "unknown opcode 0x%04X".formatted(opcode));
+        }
+        return size;
+    }
+}
diff --git a/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodePreloadVerifierService.java b/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodePreloadVerifierService.java
index 9c5f7ed2..97180080 100644
--- a/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodePreloadVerifierService.java
+++ b/prometeu-compiler/prometeu-build-pipeline/src/main/java/p/studio/compiler/backend/bytecode/BytecodePreloadVerifierService.java
@@ -35,7 +35,7 @@ public class BytecodePreloadVerifierService {
                         BytecodeMarshalingErrorCode.MARSHAL_LINKAGE_RAW_SYSCALL_IN_PRELOAD,
                         "raw syscall is forbidden in pre-load artifact");
             }
-            final var size = sizeForOpcode(opcode);
+            final var size = sizeForOpcode(opcode, pc);
             if (pc + size > end) {
                 throw new BytecodeMarshalingException(
                         BytecodeMarshalingErrorCode.MARSHAL_VERIFY_PRECHECK_TRUNCATED_INSTRUCTION,
@@ -52,13 +52,16 @@ public class BytecodePreloadVerifierService {
         }
     }
 
-    private int sizeForOpcode(final int opcode) {
-        return switch (opcode) {
-            case 0x50, 0x70, 0x71, 0x72, 0x02, 0x03, 0x04, 0x10, 0x18, 0x40, 0x41, 0x42, 0x43, 0x56 -> 6;
-            case 0x14, 0x15, 0x52, 0x54 -> 10;
-            case 0x16 -> 3;
-            default -> 2;
-        };
+    private int sizeForOpcode(
+            final int opcode,
+            final int pc) {
+        try {
+            return BytecodeOpcodeLayout.sizeForOpcode(opcode);
+        } catch (BytecodeMarshalingException ignored) {
+            throw new BytecodeMarshalingException(
+                    BytecodeMarshalingErrorCode.MARSHAL_VERIFY_PRECHECK_UNKNOWN_OPCODE,
+                    "unknown opcode 0x%04X at pc=%d".formatted(opcode, pc));
+        }
     }
 
     private int readU16(final byte[] code, final int offset) {
diff --git a/prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/backend/bytecode/BytecodeLinkPrecheckServiceTest.java b/prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/backend/bytecode/BytecodeLinkPrecheckServiceTest.java
index 44246265..17a84324 100644
--- a/prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/backend/bytecode/BytecodeLinkPrecheckServiceTest.java
+++ b/prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/backend/bytecode/BytecodeLinkPrecheckServiceTest.java
@@ -61,6 +61,21 @@ class BytecodeLinkPrecheckServiceTest {
         assertEquals(BytecodeMarshalingErrorCode.MARSHAL_VERIFY_PRECHECK_HOSTCALL_INDEX_INVALID, thrown.code());
     }
 
+    @Test
+    void validateMustRejectUnknownOpcode() {
+        final var module = new BytecodeModule(
+                0,
+                ReadOnlyList.empty(),
+                ReadOnlyList.from(new BytecodeModule.FunctionMeta(0, 4, 0, 0, 0, 1)),
+                codeUnknownThenRet(),
+                null,
+                ReadOnlyList.empty(),
+                ReadOnlyList.empty());
+
+        final var thrown = assertThrows(BytecodeMarshalingException.class, () -> service.validate(module));
+        assertEquals(BytecodeMarshalingErrorCode.MARSHAL_VERIFY_PRECHECK_UNKNOWN_OPCODE, thrown.code());
+    }
+
     private byte[] codeHostcall(final int index) {
         final var out = ByteBuffer.allocate(8).order(ByteOrder.LITTLE_ENDIAN);
         out.putShort((short) 0x71);
@@ -74,4 +89,11 @@ class BytecodeLinkPrecheckServiceTest {
         out.putShort((short) 0x51);
         return out.array();
     }
+
+    private byte[] codeUnknownThenRet() {
+        final var out = ByteBuffer.allocate(4).order(ByteOrder.LITTLE_ENDIAN);
+        out.putShort((short) 0x7FFF);
+        out.putShort((short) 0x51);
+        return out.array();
+    }
 }
diff --git a/prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/backend/bytecode/BytecodePreloadVerifierServiceTest.java b/prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/backend/bytecode/BytecodePreloadVerifierServiceTest.java
index cb77488b..3987d2d3 100644
--- a/prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/backend/bytecode/BytecodePreloadVerifierServiceTest.java
+++ b/prometeu-compiler/prometeu-build-pipeline/src/test/java/p/studio/compiler/backend/bytecode/BytecodePreloadVerifierServiceTest.java
@@ -58,6 +58,21 @@ class BytecodePreloadVerifierServiceTest {
         assertEquals(BytecodeMarshalingErrorCode.MARSHAL_VERIFY_PRECHECK_UNTERMINATED_FUNCTION, thrown.code());
     }
 
+    @Test
+    void verifyMustRejectUnknownOpcode() {
+        final var module = new BytecodeModule(
+                0,
+                ReadOnlyList.empty(),
+                ReadOnlyList.from(new BytecodeModule.FunctionMeta(0, 4, 0, 0, 0, 1)),
+                codeUnknownThenRet(),
+                null,
+                ReadOnlyList.empty(),
+                ReadOnlyList.empty());
+
+        final var thrown = assertThrows(BytecodeMarshalingException.class, () -> service.verify(module));
+        assertEquals(BytecodeMarshalingErrorCode.MARSHAL_VERIFY_PRECHECK_UNKNOWN_OPCODE, thrown.code());
+    }
+
     private byte[] codeHostcall(final int index) {
         final var out = ByteBuffer.allocate(6).order(ByteOrder.LITTLE_ENDIAN);
         out.putShort((short) 0x71);
@@ -77,4 +92,11 @@ class BytecodePreloadVerifierServiceTest {
         out.putShort((short) 0x51);
         return out.array();
     }
+
+    private byte[] codeUnknownThenRet() {
+        final var out = ByteBuffer.allocate(4).order(ByteOrder.LITTLE_ENDIAN);
+        out.putShort((short) 0x7FFF);
+        out.putShort((short) 0x51);
+        return out.array();
+    }
 }