diff --git a/oxrlib/config.py b/oxrlib/config.py
index 93eac18298f9cb5ad87781dbd1cf734a64a77438..00f6eb32357acdb37d8105a012353099fd28ab2c 100644
--- a/oxrlib/config.py
+++ b/oxrlib/config.py
@@ -6,6 +6,7 @@ import os.path
 import pathlib
 
 import babel
+import babel.dates
 import babel.numbers
 
 from . import cache, loaders
@@ -74,7 +75,7 @@ class Configuration:
             else:
                 retval -= datetime.timedelta(days=replacements['day'])
                 retval = retval.replace(**replacements)
-        return retval
+        return retval, replacements
 
     def _build_argparser(self):
         prog_parser = argparse.ArgumentParser()
@@ -191,6 +192,7 @@ class Configuration:
             return default
 
     def _post_hook_historical(self):
+        self.args.date, date_spec = self.args.date
         year = self.args.date.year
         if year < 100:
             # Don't let the user specify ambiguous dates.
@@ -223,6 +225,18 @@ class Configuration:
             self.args.to_currency = self._convert_or_error(currency_code, next_word)
         except StopIteration:
             self.args.to_currency = pref_currency
+        if ((len(date_spec) == 1)
+            and self.args.from_currency
+            and (self.args.amount is None)):
+            self.error(("ambiguous input: "
+                        "Did you want rates for {args.from_currency} on {date}, "
+                        "or to convert {amt} {args.from_currency} to {args.to_currency}?\n"
+                        "Specify more of the date to disambiguate."
+                        ).format(
+                            args=self.args,
+                            date=babel.dates.format_date(self.args.date),
+                            amt=date_spec['day'],
+                        ))
 
     def _build_cache_loader(self):
         kwargs = dict(self.conffile.items('Cache'))