diff --git a/napalm/nxos/nxos.py b/napalm/nxos/nxos.py
index b975029ef..fee5893c0 100644
--- a/napalm/nxos/nxos.py
+++ b/napalm/nxos/nxos.py
@@ -369,14 +369,18 @@ def ping(
         if source != "":
             command += " source {}".format(source)
         elif source_interface != "":
-            command += " source {}".format(source_interface)
-
-        if vrf != "":
-            command += " vrf {}".format(vrf)
+            command += " source-interface {}".format(source_interface)
+
+        # source_interface and vrf are mutually exclusive, but since they
+        # provide the same behavior, no need to raise an exception--just
+        # prefer source_interface.
+        if not source_interface:
+            if vrf != "":
+                command += " vrf {}".format(vrf)
         output = self._send_command(command, raw_text=True)
         assert isinstance(output, str)
 
-        if "connect:" in output:
+        if "connect:" in output.lower() or "invalid" in output.lower():
             ping_dict["error"] = output
         elif "PING" in output:
             ping_dict["success"] = {