diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -460,7 +460,10 @@
                 "outputs",
                 RPCArg::Type::ARR,
                 RPCArg::Optional::NO,
-                "a json array with outputs (key-value pairs).\n"
+                "a json array with outputs (key-value pairs), where none of "
+                "the keys are duplicated.\n"
+                "That is, each address can only appear once and there can only "
+                "be one 'data' object.\n"
                 "For compatibility reasons, a dictionary, which holds the "
                 "key-value pairs directly, is also\n"
                 "                             accepted as second parameter.",
@@ -1518,7 +1521,10 @@
                 "outputs",
                 RPCArg::Type::ARR,
                 RPCArg::Optional::NO,
-                "a json array with outputs (key-value pairs).\n"
+                "a json array with outputs (key-value pairs), where none of "
+                "the keys are duplicated.\n"
+                "That is, each address can only appear once and there can only "
+                "be one 'data' object.\n"
                 "For compatibility reasons, a dictionary, which holds the "
                 "key-value pairs directly, is also\n"
                 "                             accepted as second parameter.",
diff --git a/src/rpc/rawtransaction_util.cpp b/src/rpc/rawtransaction_util.cpp
--- a/src/rpc/rawtransaction_util.cpp
+++ b/src/rpc/rawtransaction_util.cpp
@@ -89,7 +89,6 @@
         rawTx.vin.push_back(in);
     }
 
-    std::set<CTxDestination> destinations;
     if (!outputs_is_obj) {
         // Translate array of key-value pairs into dict
         UniValue outputs_dict = UniValue(UniValue::VOBJ);
@@ -109,8 +108,18 @@
         }
         outputs = std::move(outputs_dict);
     }
+
+    // Duplicate checking
+    std::set<CTxDestination> destinations;
+    bool has_data{false};
+
     for (const std::string &name_ : outputs.getKeys()) {
         if (name_ == "data") {
+            if (has_data) {
+                throw JSONRPCError(RPC_INVALID_PARAMETER,
+                                   "Invalid parameter, duplicate key: data");
+            }
+            has_data = true;
             std::vector<uint8_t> data =
                 ParseHexV(outputs[name_].getValStr(), "Data");
 
diff --git a/src/test/rpc_tests.cpp b/src/test/rpc_tests.cpp
--- a/src/test/rpc_tests.cpp
+++ b/src/test/rpc_tests.cpp
@@ -203,14 +203,6 @@
                 "\"a3b807410df0b60fcb9736768df5823938b2f838694939ba45f3c0a1bff1"
                 "50ed\",\"vout\":0}] {\"data\":\"68656c6c6f776f726c64\"}"));
 
-    // Allow more than one data transaction output
-    BOOST_CHECK_NO_THROW(CallRPC("createrawtransaction "
-                                 "[{\"txid\":"
-                                 "\"a3b807410df0b60fcb9736768df5823938b2f838694"
-                                 "939ba45f3c0a1bff150ed\",\"vout\":0}] "
-                                 "{\"data\":\"68656c6c6f776f726c64\",\"data\":"
-                                 "\"68656c6c6f776f726c64\"}"));
-
     // Key not "data" (bad address)
     BOOST_CHECK_THROW(
         CallRPC("createrawtransaction "
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -4567,7 +4567,10 @@
                 "outputs",
                 RPCArg::Type::ARR,
                 RPCArg::Optional::NO,
-                "a json array with outputs (key-value pairs).\n"
+                "a json array with outputs (key-value pairs), where none of "
+                "the keys are duplicated.\n"
+                "That is, each address can only appear once and there can only "
+                "be one 'data' object.\n"
                 "For compatibility reasons, a dictionary, which holds the "
                 "key-value pairs directly, is also\n"
                 "                             accepted as second parameter.",
diff --git a/test/functional/rpc_rawtransaction.py b/test/functional/rpc_rawtransaction.py
--- a/test/functional/rpc_rawtransaction.py
+++ b/test/functional/rpc_rawtransaction.py
@@ -147,6 +147,20 @@
             address), self.nodes[0].createrawtransaction, [], multidict([(address, 1), (address, 1)]))
         assert_raises_rpc_error(-8, "Invalid parameter, duplicated address: {}".format(
             address), self.nodes[0].createrawtransaction, [], [{address: 1}, {address: 1}])
+        assert_raises_rpc_error(-8,
+                                "Invalid parameter, duplicate key: data",
+                                self.nodes[0].createrawtransaction,
+                                [],
+                                [{"data": 'aa'},
+                                    {"data": "bb"}])
+        assert_raises_rpc_error(-8,
+                                "Invalid parameter, duplicate key: data",
+                                self.nodes[0].createrawtransaction,
+                                [],
+                                multidict([("data",
+                                            'aa'),
+                                           ("data",
+                                            "bb")]))
         assert_raises_rpc_error(-8, "Invalid parameter, key-value pair must contain exactly one key",
                                 self.nodes[0].createrawtransaction, [], [{'a': 1, 'b': 2}])
         assert_raises_rpc_error(-8, "Invalid parameter, key-value pair not an object as expected",
@@ -181,23 +195,14 @@
             self.nodes[2].createrawtransaction(inputs=[{'txid': txid, 'vout': 9}], outputs=[
                                                {address: 99}, {address2: 99}]),
         )
-        # Two data outputs
-        tx.deserialize(BytesIO(hex_str_to_bytes(self.nodes[2].createrawtransaction(inputs=[
-                       {'txid': txid, 'vout': 9}], outputs=multidict([('data', '99'), ('data', '99')])))))
-        assert_equal(len(tx.vout), 2)
-        assert_equal(
-            tx.serialize().hex(),
-            self.nodes[2].createrawtransaction(inputs=[{'txid': txid, 'vout': 9}], outputs=[
-                                               {'data': '99'}, {'data': '99'}]),
-        )
         # Multiple mixed outputs
         tx.deserialize(BytesIO(hex_str_to_bytes(self.nodes[2].createrawtransaction(inputs=[
-                       {'txid': txid, 'vout': 9}], outputs=multidict([(address, 99), ('data', '99'), ('data', '99')])))))
+                       {'txid': txid, 'vout': 9}], outputs=multidict([(address, 99), (address2, 99), ('data', '99')])))))
         assert_equal(len(tx.vout), 3)
         assert_equal(
             tx.serialize().hex(),
             self.nodes[2].createrawtransaction(inputs=[{'txid': txid, 'vout': 9}], outputs=[
-                                               {address: 99}, {'data': '99'}, {'data': '99'}]),
+                                               {address: 99}, {address2: 99}, {'data': '99'}]),
         )
 
         self.log.info('sendrawtransaction with missing input')