diff --git a/oxrlib/config.py b/oxrlib/config.py
index e85cb3aa4a02d3dcf00b4bd0665cf9425fa20e9b..682a5500a4ca017f993ae82e5ff14349738139e3 100644
--- a/oxrlib/config.py
+++ b/oxrlib/config.py
@@ -123,17 +123,17 @@ class Configuration:
             "If you omit the year or month, it fills in the current year/month."
         )
         hist_parser.add_argument(
-            'word1', nargs='?', metavar='first code',
-            help="Convert or show rates from this currency, in three-letter code format. "
-            "If not specified, show all rates on the given date.",
+            'word1', nargs='?', metavar='amount',
+            help="Convert this amount of currency. If not specified, show rates.",
         )
         hist_parser.add_argument(
-            'word2', nargs='?', metavar='amount',
-            help="Convert this amount of currency. If not specified, show rates.",
+            'word2', nargs='?', metavar='first code',
+            help="Convert or show rates from this currency, in three-letter code format. "
+            "If not specified, show all rates on the given date.",
         )
         hist_parser.add_argument(
             'word3', nargs='?', metavar='second code',
-            help="Convert to this currency, in three-letter code format. "
+            help="Convert or show rates to this currency, in three-letter code format. "
             "If not specified, defaults to the base currency.",
         )
         hist_parser.add_argument('word4', nargs='?', help=argparse.SUPPRESS)
@@ -184,21 +184,25 @@ class Configuration:
                                  currency_list, convert_fallback=True)
         self._read_from_conffile('ledger', 'Historical', False, getter='getboolean')
         self.args.to_currency = self.args.base
-        if self.args.word4 and (self.args.word3.lower() in self.PREPOSITIONS):
-            self.args.word3 = self.args.word4
-        if self.args.word1 is None:
+        raw_words = iter(getattr(self.args, 'word' + c) for c in '1234')
+        words = iter(word for word in raw_words if word is not None)
+        try:
+            next_word = next(words)
+            try:
+                self.args.amount = decimal.Decimal(next_word)
+            except decimal.InvalidOperation:
+                pass
+            else:
+                # If an amount was given, a currency code must be given too.
+                # If it wasn't, set a value that can't be parsed as a currency.
+                next_word = next(words, 'none given')
+            self.args.from_currency = self._convert_or_error(currency_code, next_word)
+            next_word = next(words)
+            if next_word.lower() in self.PREPOSITIONS:
+                next_word = next(words, next_word)
+            self.args.to_currency = self._convert_or_error(currency_code, next_word)
+        except StopIteration:
             pass
-        elif self.args.word2 is None:
-            self.args.from_currency = self._convert_or_error(
-                currency_code, self.args.word1)
-        else:
-            self.args.amount = self._convert_or_error(
-                decimal.Decimal, self.args.word1)
-            self.args.from_currency = self._convert_or_error(
-                currency_code, self.args.word2)
-            if self.args.word3 is not None:
-                self.args.to_currency = self._convert_or_error(
-                    currency_code, self.args.word3 or self.args.base)
 
     def _build_cache_loader(self):
         kwargs = dict(self.conffile.items('Cache'))