diff --git a/test/functional/rpc_psbt.py b/test/functional/rpc_psbt.py
index c678eb4768..d41571d3ba 100755
--- a/test/functional/rpc_psbt.py
+++ b/test/functional/rpc_psbt.py
@@ -514,20 +514,15 @@ class PSBTTest(BitcoinTestFramework):
         self.nodes[0].decodepsbt(new_psbt)
 
         # Make sure that a non-psbt with signatures cannot be converted
-        # Error could be either "TX decode failed" (segwit inputs causes parsing to fail) or "Inputs must not have scriptSigs and scriptWitnesses"
-        # We must set iswitness=True because the serialized transaction has inputs and is therefore a witness transaction
         signedtx = self.nodes[0].signrawtransactionwithwallet(rawtx['hex'])
-        # Can be either a scriptSig or a scriptWitness that it yells about, depending on which UTXOs are selected for the TX
-        assert_raises_rpc_error(-22, "Inputs must not have", self.nodes[0].converttopsbt, signedtx['hex'], False)
-        assert_raises_rpc_error(-22, "Inputs must not have", self.nodes[0].converttopsbt, signedtx['hex'])
-        assert_raises_rpc_error(-22, "", self.nodes[0].converttopsbt, hexstring=signedtx['hex'], iswitness=True)
-        assert_raises_rpc_error(-22, "", self.nodes[0].converttopsbt, hexstring=signedtx['hex'], permitsigdata=False, iswitness=True)
+        assert_raises_rpc_error(-22, "Inputs must not have scriptWitnesses",
+                                self.nodes[0].converttopsbt, hexstring=signedtx['hex'])  # permitsigdata=False by default
+        assert_raises_rpc_error(-22, "Inputs must not have scriptWitnesses",
+                                self.nodes[0].converttopsbt, hexstring=signedtx['hex'], permitsigdata=False)
+        assert_raises_rpc_error(-22, "Inputs must not have scriptWitnesses",
+                                self.nodes[0].converttopsbt, hexstring=signedtx['hex'], permitsigdata=False, iswitness=True)
         # Unless we allow it to convert and strip signatures
-        self.nodes[0].converttopsbt(signedtx['hex'], True)
-
-        # Explicitly allow converting non-empty txs
-        new_psbt = self.nodes[0].converttopsbt(rawtx['hex'])
-        self.nodes[0].decodepsbt(new_psbt)
+        self.nodes[0].converttopsbt(hexstring=signedtx['hex'], permitsigdata=True)
 
         # Create outputs to nodes 1 and 2
         # We do a whole song-and-dance here (instead of calling sendtoaddress) to get access to the unblinded transaction data to find our outputs