diff --git a/src/psbt.h b/src/psbt.h
index 21daa050ea0..a752e99e749 100644
--- a/src/psbt.h
+++ b/src/psbt.h
@@ -69,52 +69,52 @@ struct PSBTInput
     inline void Serialize(Stream& s) const {
         // Write the utxo
         if (non_witness_utxo) {
-            SerializeToVector(s, PSBT_IN_NON_WITNESS_UTXO);
+            SerializeToVector(s, CompactSizeWriter(PSBT_IN_NON_WITNESS_UTXO));
             OverrideStream<Stream> os(&s, s.GetType(), s.GetVersion() | SERIALIZE_TRANSACTION_NO_WITNESS);
             SerializeToVector(os, non_witness_utxo);
         }
         if (!witness_utxo.IsNull()) {
-            SerializeToVector(s, PSBT_IN_WITNESS_UTXO);
+            SerializeToVector(s, CompactSizeWriter(PSBT_IN_WITNESS_UTXO));
             SerializeToVector(s, witness_utxo);
         }
 
         if (final_script_sig.empty() && final_script_witness.IsNull()) {
             // Write any partial signatures
             for (auto sig_pair : partial_sigs) {
-                SerializeToVector(s, PSBT_IN_PARTIAL_SIG, Span{sig_pair.second.first});
+                SerializeToVector(s, CompactSizeWriter(PSBT_IN_PARTIAL_SIG), Span{sig_pair.second.first});
                 s << sig_pair.second.second;
             }
 
             // Write the sighash type
             if (sighash_type != std::nullopt) {
-                SerializeToVector(s, PSBT_IN_SIGHASH);
+                SerializeToVector(s, CompactSizeWriter(PSBT_IN_SIGHASH));
                 SerializeToVector(s, *sighash_type);
             }
 
             // Write the redeem script
             if (!redeem_script.empty()) {
-                SerializeToVector(s, PSBT_IN_REDEEMSCRIPT);
+                SerializeToVector(s, CompactSizeWriter(PSBT_IN_REDEEMSCRIPT));
                 s << redeem_script;
             }
 
             // Write the witness script
             if (!witness_script.empty()) {
-                SerializeToVector(s, PSBT_IN_WITNESSSCRIPT);
+                SerializeToVector(s, CompactSizeWriter(PSBT_IN_WITNESSSCRIPT));
                 s << witness_script;
             }
 
             // Write any hd keypaths
-            SerializeHDKeypaths(s, hd_keypaths, PSBT_IN_BIP32_DERIVATION);
+            SerializeHDKeypaths(s, hd_keypaths, CompactSizeWriter(PSBT_IN_BIP32_DERIVATION));
         }
 
         // Write script sig
         if (!final_script_sig.empty()) {
-            SerializeToVector(s, PSBT_IN_SCRIPTSIG);
+            SerializeToVector(s, CompactSizeWriter(PSBT_IN_SCRIPTSIG));
             s << final_script_sig;
         }
         // write script witness
         if (!final_script_witness.IsNull()) {
-            SerializeToVector(s, PSBT_IN_SCRIPTWITNESS);
+            SerializeToVector(s, CompactSizeWriter(PSBT_IN_SCRIPTWITNESS));
             SerializeToVector(s, final_script_witness.stack);
         }
 
@@ -147,8 +147,9 @@ struct PSBTInput
                 break;
             }
 
-            // First byte of key is the type
-            unsigned char type = key[0];
+            // Type is compact size uint at beginning of key
+            SpanReader skey(s.GetType(), s.GetVersion(), key);
+            uint64_t type = ReadCompactSize(skey);
 
             // Do stuff based on type
             switch(type) {
@@ -292,18 +293,18 @@ struct PSBTOutput
     inline void Serialize(Stream& s) const {
         // Write the redeem script
         if (!redeem_script.empty()) {
-            SerializeToVector(s, PSBT_OUT_REDEEMSCRIPT);
+            SerializeToVector(s, CompactSizeWriter(PSBT_OUT_REDEEMSCRIPT));
             s << redeem_script;
         }
 
         // Write the witness script
         if (!witness_script.empty()) {
-            SerializeToVector(s, PSBT_OUT_WITNESSSCRIPT);
+            SerializeToVector(s, CompactSizeWriter(PSBT_OUT_WITNESSSCRIPT));
             s << witness_script;
         }
 
         // Write any hd keypaths
-        SerializeHDKeypaths(s, hd_keypaths, PSBT_OUT_BIP32_DERIVATION);
+        SerializeHDKeypaths(s, hd_keypaths, CompactSizeWriter(PSBT_OUT_BIP32_DERIVATION));
 
         // Write unknown things
         for (auto& entry : unknown) {
@@ -334,8 +335,9 @@ struct PSBTOutput
                 break;
             }
 
-            // First byte of key is the type
-            unsigned char type = key[0];
+            // Type is compact size uint at beginning of key
+            SpanReader skey(s.GetType(), s.GetVersion(), key);
+            uint64_t type = ReadCompactSize(skey);
 
             // Do stuff based on type
             switch(type) {
@@ -422,7 +424,7 @@ struct PartiallySignedTransaction
         s << PSBT_MAGIC_BYTES;
 
         // unsigned tx flag
-        SerializeToVector(s, PSBT_GLOBAL_UNSIGNED_TX);
+        SerializeToVector(s, CompactSizeWriter(PSBT_GLOBAL_UNSIGNED_TX));
 
         // Write serialized tx to a stream
         OverrideStream<Stream> os(&s, s.GetType(), s.GetVersion() | SERIALIZE_TRANSACTION_NO_WITNESS);
@@ -474,8 +476,9 @@ struct PartiallySignedTransaction
                 break;
             }
 
-            // First byte of key is the type
-            unsigned char type = key[0];
+            // Type is compact size uint at beginning of key
+            SpanReader skey(s.GetType(), s.GetVersion(), key);
+            uint64_t type = ReadCompactSize(skey);
 
             // Do stuff based on type
             switch(type) {
diff --git a/src/script/sign.h b/src/script/sign.h
index 50525af3323..622147cd95b 100644
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -143,7 +143,7 @@ void DeserializeHDKeypaths(Stream& s, const std::vector<unsigned char>& key, std
 
 // Serialize HD keypaths to a stream from a map
 template<typename Stream>
-void SerializeHDKeypaths(Stream& s, const std::map<CPubKey, KeyOriginInfo>& hd_keypaths, uint8_t type)
+void SerializeHDKeypaths(Stream& s, const std::map<CPubKey, KeyOriginInfo>& hd_keypaths, CompactSizeWriter type)
 {
     for (auto keypath_pair : hd_keypaths) {
         if (!keypath_pair.first.IsValid()) {
diff --git a/src/serialize.h b/src/serialize.h
index edf10440c65..873361fe9e9 100644
--- a/src/serialize.h
+++ b/src/serialize.h
@@ -527,6 +527,19 @@ struct CompactSizeFormatter
     }
 };
 
+class CompactSizeWriter
+{
+protected:
+    uint64_t n;
+public:
+    explicit CompactSizeWriter(uint64_t n_in) : n(n_in) { }
+
+    template<typename Stream>
+    void Serialize(Stream &s) const {
+        WriteCompactSize<Stream>(s, n);
+    }
+};
+
 template<size_t Limit>
 struct LimitedStringFormatter
 {
diff --git a/src/test/fuzz/script_sign.cpp b/src/test/fuzz/script_sign.cpp
index 79380bd9c9a..205f6c80617 100644
--- a/src/test/fuzz/script_sign.cpp
+++ b/src/test/fuzz/script_sign.cpp
@@ -43,7 +43,7 @@ FUZZ_TARGET_INIT(script_sign, initialize_script_sign)
         } catch (const std::ios_base::failure&) {
         }
         CDataStream serialized{SER_NETWORK, PROTOCOL_VERSION};
-        SerializeHDKeypaths(serialized, hd_keypaths, fuzzed_data_provider.ConsumeIntegral<uint8_t>());
+        SerializeHDKeypaths(serialized, hd_keypaths, CompactSizeWriter(fuzzed_data_provider.ConsumeIntegral<uint8_t>()));
     }
 
     {
@@ -61,7 +61,7 @@ FUZZ_TARGET_INIT(script_sign, initialize_script_sign)
         }
         CDataStream serialized{SER_NETWORK, PROTOCOL_VERSION};
         try {
-            SerializeHDKeypaths(serialized, hd_keypaths, fuzzed_data_provider.ConsumeIntegral<uint8_t>());
+            SerializeHDKeypaths(serialized, hd_keypaths, CompactSizeWriter(fuzzed_data_provider.ConsumeIntegral<uint8_t>()));
         } catch (const std::ios_base::failure&) {
         }
         std::map<CPubKey, KeyOriginInfo> deserialized_hd_keypaths;