diff --git a/external/pegmatite b/external/pegmatite
index 726cad86f..42fd31fcf 160000
--- a/external/pegmatite
+++ b/external/pegmatite
@@ -1 +1 @@
-Subproject commit 726cad86f8d822f762099962cf2601936791eec7
+Subproject commit 42fd31fcfc4c3ad8225c40c6e88b4174711ffe98
diff --git a/src/compiler/codegen/codegen.cc b/src/compiler/codegen/codegen.cc
index 70ca364f2..d373fe300 100644
--- a/src/compiler/codegen/codegen.cc
+++ b/src/compiler/codegen/codegen.cc
@@ -92,6 +92,15 @@ namespace verona::compiler
     return std::make_pair(class_item, method_item);
   }
 
+  /**
+   * Writes the magic numbers to the bytecode
+   * @param code Generator to which the bytes should be emitted
+   */
+  void write_magic_number(Generator& code)
+  {
+    code.u32(bytecode::MAGIC_NUMBER);
+  }
+
   std::vector<uint8_t> codegen(
     Context& context, const Program& program, const AnalysisResults& analysis)
   {
@@ -100,7 +109,9 @@ namespace verona::compiler
       return {};
 
     std::vector<uint8_t> code;
+
     Generator gen(code);
+    write_magic_number(gen);
 
     Reachability reachability = compute_reachability(
       context, program, gen, entry->first, entry->second, analysis);
diff --git a/src/interpreter/bytecode.h b/src/interpreter/bytecode.h
index 7c97930d1..5815a556d 100644
--- a/src/interpreter/bytecode.h
+++ b/src/interpreter/bytecode.h
@@ -13,6 +13,7 @@
  * Bytecode has the following layout:
  *
  * Program header:
+ * - 32-bit verona magic number, equal to the MAGIC_NUMBER constant
  * - 32-bit number of descriptors, followed by that many descriptors (see below)
  * - 32-bit descriptor index of Main class
  * - 32-bit selector index of main method
@@ -131,6 +132,8 @@ namespace verona::bytecode
     uint32_t size;
   };
 
+  constexpr static uint32_t MAGIC_NUMBER = 0xF38932C3;
+
   /**
    * Type-safe wrapper for register indices, helps avoid implicit conversion
    * from/to integers.
diff --git a/src/interpreter/code.h b/src/interpreter/code.h
index 16051ac1d..2472280b7 100644
--- a/src/interpreter/code.h
+++ b/src/interpreter/code.h
@@ -86,10 +86,12 @@ namespace verona::interpreter
     {
       return load<int16_t>(ip);
     }
-    uint16_t u32(size_t& ip) const
+
+    uint32_t u32(size_t& ip) const
     {
       return load<uint32_t>(ip);
     }
+
     uint64_t u64(size_t& ip) const
     {
       return load<uint64_t>(ip);
@@ -137,6 +139,8 @@ namespace verona::interpreter
     {
       size_t ip = 0;
 
+      check_verona_nums(ip);
+
       uint32_t descriptors_count = u32(ip);
       for (uint32_t i = 0; i < descriptors_count; i++)
       {
@@ -190,6 +194,15 @@ namespace verona::interpreter
 
     SpecialDescriptors special_descriptors_;
 
+    void check_verona_nums(size_t& ip)
+    {
+      uint32_t nums = u32(ip);
+      if (nums != bytecode::MAGIC_NUMBER)
+      {
+        throw std::logic_error{"Invalid magic number, not recognized"};
+      }
+    }
+
     std::unique_ptr<VMDescriptor> load_descriptor(size_t& ip)
     {
       std::string_view name = str(ip);