Throw parsing error if prefix query contains multiple fields in its short version

core/src/main/java/org/elasticsearch/index/query/PrefixQueryBuilder.java

@@ -158,6 +158,10 @@ public class PrefixQueryBuilder extends AbstractQueryBuilder<PrefixQueryBuilder>
                     }
                 }
             } else {
+                if (fieldName != null) {
+                    throw new ParsingException(parser.getTokenLocation(), "[prefix] query doesn't support multiple fields, found ["
+                            + fieldName + "] and [" + parser.currentName() + "]");
+                }
                 fieldName = currentFieldName;
                 value = parser.textOrNull();
             }

core/src/test/java/org/elasticsearch/index/query/PrefixQueryBuilderTests.java

@@ -127,5 +127,15 @@ public class PrefixQueryBuilderTests extends AbstractQueryTestCase<PrefixQueryBu
                 "}";
         ParsingException e = expectThrows(ParsingException.class, () -> parseQuery(json));
         assertEquals("[prefix] query doesn't support multiple fields, found [user1] and [user2]", e.getMessage());
+
+        String shortJson =
+                "{\n" +
+                "    \"prefix\": {\n" +
+                "      \"user1\": \"ki\",\n" +
+                "      \"user2\": \"ki\"\n" +
+                "    }\n" +
+                "}";
+        e = expectThrows(ParsingException.class, () -> parseQuery(shortJson));
+        assertEquals("[prefix] query doesn't support multiple fields, found [user1] and [user2]", e.getMessage());
     }
 }