diff --git a/src/psbt.h b/src/psbt.h
--- a/src/psbt.h
+++ b/src/psbt.h
@@ -100,6 +100,9 @@
     }
 
     template <typename Stream> inline void Unserialize(Stream &s) {
+        // Used for duplicate key detection
+        std::set<std::vector<uint8_t>> key_lookup;
+
         // Read loop
         bool found_sep = false;
         while (!s.empty()) {
@@ -121,7 +124,7 @@
             // Do stuff based on type
             switch (type) {
                 case PSBT_IN_UTXO:
-                    if (!utxo.IsNull()) {
+                    if (!key_lookup.emplace(key).second) {
                         throw std::ios_base::failure(
                             "Duplicate Key, input utxo already provided");
                     } else if (key.size() != 1) {
@@ -159,7 +162,7 @@
                     break;
                 }
                 case PSBT_IN_SIGHASH:
-                    if (sighash_type.getRawSigHashType() != 0) {
+                    if (!key_lookup.emplace(key).second) {
                         throw std::ios_base::failure(
                             "Duplicate Key, input sighash type already "
                             "provided");
@@ -170,7 +173,7 @@
                     UnserializeFromVector(s, sighash_type);
                     break;
                 case PSBT_IN_REDEEMSCRIPT: {
-                    if (!redeem_script.empty()) {
+                    if (!key_lookup.emplace(key).second) {
                         throw std::ios_base::failure(
                             "Duplicate Key, input redeemScript already "
                             "provided");
@@ -187,7 +190,7 @@
                     break;
                 }
                 case PSBT_IN_SCRIPTSIG: {
-                    if (!final_script_sig.empty()) {
+                    if (!key_lookup.emplace(key).second) {
                         throw std::ios_base::failure(
                             "Duplicate Key, input final scriptSig already "
                             "provided");
@@ -256,6 +259,9 @@
     }
 
     template <typename Stream> inline void Unserialize(Stream &s) {
+        // Used for duplicate key detection
+        std::set<std::vector<uint8_t>> key_lookup;
+
         // Read loop
         bool found_sep = false;
         while (!s.empty()) {
@@ -277,7 +283,7 @@
             // Do stuff based on type
             switch (type) {
                 case PSBT_OUT_REDEEMSCRIPT: {
-                    if (!redeem_script.empty()) {
+                    if (!key_lookup.emplace(key).second) {
                         throw std::ios_base::failure(
                             "Duplicate Key, output redeemScript already "
                             "provided");
@@ -392,6 +398,9 @@
             throw std::ios_base::failure("Invalid PSBT magic bytes");
         }
 
+        // Used for duplicate key detection
+        std::set<std::vector<uint8_t>> key_lookup;
+
         // Read global data
         bool found_sep = false;
         while (!s.empty()) {
@@ -413,7 +422,7 @@
             // Do stuff based on type
             switch (type) {
                 case PSBT_GLOBAL_UNSIGNED_TX: {
-                    if (tx) {
+                    if (!key_lookup.emplace(key).second) {
                         throw std::ios_base::failure(
                             "Duplicate Key, unsigned tx already provided");
                     } else if (key.size() != 1) {
diff --git a/test/functional/data/rpc_psbt.json b/test/functional/data/rpc_psbt.json
--- a/test/functional/data/rpc_psbt.json
+++ b/test/functional/data/rpc_psbt.json
@@ -15,7 +15,15 @@
         "cHNidP8BAHMCAAAAATAa6YblFqHsisW0vGVz0y+DtGXiOtdhZ9aLOOcwtNvbAAAAAAD/////AnR7AQAAAAAAF6kUA6oXrogrXQ1Usl1jEE5P/s57nqKHYEOZOwAAAAAXqRS5IbG6b3IuS/qDtlV6MTmYakLsg4cAAAAAAAEAHwDKmjsAAAAAFgAU0tlLZK4IWH7vyO6xh8YB6Tn5A3wCAwAEQQAAAAABABYAFGLp6YL/803YI5YQMWsJDNKjt0fLAAEAIgAgh2utgy8dFoAV7UEjKp6mWhgV2e8TwO+HWfZLWysnimUBASVRIQO3ziOgHFtL8ApkJTfN+rsxW2aDMoZ0eO9RMJ0r1X+Kh1GuAA==",
         "cHNidP8BAHMCAAAAATAa6YblFqHsisW0vGVz0y+DtGXiOtdhZ9aLOOcwtNvbAAAAAAD/////AnR7AQAAAAAAF6kUA6oXrogrXQ1Usl1jEE5P/s57nqKHYEOZOwAAAAAXqRS5IbG6b3IuS/qDtlV6MTmYakLsg4cAAAAAAAACAAAWABRi6emC//NN2COWEDFrCQzSo7dHywACAAAiACCHa62DLx0WgBXtQSMqnqZaGBXZ7xPA74dZ9ktbKyeKZQEBJVEhA7fOI6AcW0vwCmQlN836uzFbZoMyhnR471EwnSvVf4qHUa4A",
         "cHNidP8BAHMCAAAAATAa6YblFqHsisW0vGVz0y+DtGXiOtdhZ9aLOOcwtNvbAAAAAAD/////AnR7AQAAAAAAF6kUA6oXrogrXQ1Usl1jEE5P/s57nqKHYEOZOwAAAAAXqRS5IbG6b3IuS/qDtlV6MTmYakLsg4cAAAAAAAEBHwDKmjsAAAAAFgAU0tlLZK4IWH7vyO6xh8YB6Tn5A3wAAQAWABRi6emC//NN2COWEDFrCQzSo7dHywABACIAIIdrrYMvHRaAFe1BIyqeploYFdnvE8Dvh1n2S1srJ4plIQEAJVEhA7fOI6AcW0vwCmQlN836uzFbZoMyhnR471EwnSvVf4qHUa4A",
-        "cHNidP8BAHMCAAAAAbiWoY6pOQepFsEGhUPXaulX9rvye2NH+NrdlAHg+WgpAQAAAAD/////AkBLTAAAAAAAF6kUqWwXCcLM5BN2zoNqMNT5qMlIi7+HQEtMAAAAAAAXqRSVF/in2XNxAlN1OSxkyp0z+Wtg2YcAAAAAAAEBIBNssgAAAAAAF6kUamsvautR8hRlMRY6OKNTx03DK96HAQcXFgAUo8u1LWpHprjt/uENAwBpGZD0UH0BCGsCRzBEAiAONfH3DYiw67ZbylrsxCF/XXpVwyWBRgofyRbPslzvwgIgIKCsWw5sHSIPh1icNvcVLZLHWj6NA7Dk+4Os2pOnMbQBIQPGStfYHPtyhpV7zIWtn0Q4GXv5gK1zy/tnJ+cBXu4iiwABABYAFMwmJQEz+HDpBEEabxJ5PogPsqZRAAEAFgAUyCrGc3h3FYCmiIspbv2pSTKZ5jU"
+        "cHNidP8BAHMCAAAAAbiWoY6pOQepFsEGhUPXaulX9rvye2NH+NrdlAHg+WgpAQAAAAD/////AkBLTAAAAAAAF6kUqWwXCcLM5BN2zoNqMNT5qMlIi7+HQEtMAAAAAAAXqRSVF/in2XNxAlN1OSxkyp0z+Wtg2YcAAAAAAAEBIBNssgAAAAAAF6kUamsvautR8hRlMRY6OKNTx03DK96HAQcXFgAUo8u1LWpHprjt/uENAwBpGZD0UH0BCGsCRzBEAiAONfH3DYiw67ZbylrsxCF/XXpVwyWBRgofyRbPslzvwgIgIKCsWw5sHSIPh1icNvcVLZLHWj6NA7Dk+4Os2pOnMbQBIQPGStfYHPtyhpV7zIWtn0Q4GXv5gK1zy/tnJ+cBXu4iiwABABYAFMwmJQEz+HDpBEEabxJ5PogPsqZRAAEAFgAUyCrGc3h3FYCmiIspbv2pSTKZ5jU",
+        "cHNidP8BACoCAAAAAAFAQg8AAAAAABepFG6Rty1Vk+fUOR4v9E6R6YXDFkHwhwAAAAAAAQEAAQEBagA=",
+        "cHNidP8BACoCAAAAAAFAQg8AAAAAABepFG6Rty1Vk+fUOR4v9E6R6YXDFkHwhwAAAAAAAQAAAQABagA=",
+        "cHNidP8BADMBAAAAAREREREREREREREREREREREREfrK3hERERERERERERERfwAAAAD/////AAAAAAAAAQEJ//////////8AAQEJAADK/gAAAAAAAA==",
+        "cHNidP8BADMBAAAAAREREREREREREREREREREREREfrK3hERERERERERERERfwAAAAD/////AAAAAAAAAQMErd7f7gEDBAEAAAAA",
+        "cHNidP8BADMBAAAAAREREREREREREREREREREREREfrK3hERERERERERERERfwAAAAD/////AAAAAAAAAQQAAQQBagA=",
+        "cHNidP8BADMBAAAAAREREREREREREREREREREREREfrK3hERERERERERERERfwAAAAD/////AAAAAAAAAQEJAOH1BQAAAAAAAQUAAQUBUQA=",
+        "cHNidP8BADMBAAAAAREREREREREREREREREREREREfrK3hERERERERERERERfwAAAAD/////AAAAAAAAAQcAAQcBUQA=",
+        "cHNidP8BADMBAAAAAREREREREREREREREREREREREfrK3hERERERERERERERfwAAAAD/////AAAAAAAAAQEJAOH1BQAAAAAAAQgBAAEIAwEBUQA="
     ],
     "valid" : [
         "cHNidP8BAHUCAAAAASaBcTce3/KF6Tet7qSze3gADAVmy7OtZGQXE8pCFxv2AAAAAAD+////AtPf9QUAAAAAGXapFNDFmQPFusKGh2DpD9UhpGZap2UgiKwA4fUFAAAAABepFDVF5uM7gyxHBQ8k0+65PJwDlIvHh7MuEwAAAQAiAMLrCwAAAAAZdqkUhc/xCX/Z4Ai7NK9wnGIZeziXikiIrAAAAA==",