diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -1675,15 +1675,15 @@
 
     // parse hex string from parameter
     CMutableTransaction tx;
+    bool permitsigdata =
+        request.params[1].isNull() ? false : request.params[1].get_bool();
     if (!DecodeHexTx(tx, request.params[0].get_str())) {
         throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed");
     }
 
     // Remove all scriptSigs from inputs
     for (CTxIn &input : tx.vin) {
-        if (!input.scriptSig.empty() &&
-            (request.params[1].isNull() ||
-             (!request.params[1].isNull() && request.params[1].get_bool()))) {
+        if (!input.scriptSig.empty() && !permitsigdata) {
             throw JSONRPCError(RPC_DESERIALIZATION_ERROR,
                                "Inputs must not have scriptSigs");
         }
diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -106,6 +106,13 @@
         new_psbt = self.nodes[0].converttopsbt(rawtx['hex'])
         self.nodes[0].decodepsbt(new_psbt)
 
+        # Make sure that a psbt with signatures cannot be converted
+        signedtx = self.nodes[0].signrawtransactionwithwallet(rawtx['hex'])
+        assert_raises_rpc_error(-22, "Inputs must not have scriptSigs",
+                                self.nodes[0].converttopsbt, signedtx['hex'])
+        # Unless we allow it to convert and strip signatures
+        self.nodes[0].converttopsbt(signedtx['hex'], True)
+
         # Explicilty allow converting non-empty txs
         new_psbt = self.nodes[0].converttopsbt(rawtx['hex'])
         self.nodes[0].decodepsbt(new_psbt)