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'))
diff --git a/setup.py b/setup.py
index c287242cb0857a92b3c21330b0b71de9029ceaa2..5375d839c3d659a66c732636fc4cfe7cac96ace3 100755
--- a/setup.py
+++ b/setup.py
@@ -5,7 +5,7 @@ from setuptools import setup
 setup(
     name='oxrlib',
     description="Library to query the Open Exchange Rates (OXR) API",
-    version='1.6',
+    version='1.7',
     author='Brett Smith',
     author_email='brettcsmith@brettcsmith.org',
     license='GNU AGPLv3+',
diff --git a/tests/test_Configuration.py b/tests/test_Configuration.py
index 4c85edbe40c8640b3dc15e843bf21ec234286843..7529a9f764774a0a297e6e3ca9c76523b99e22c6 100644
--- a/tests/test_Configuration.py
+++ b/tests/test_Configuration.py
@@ -128,3 +128,12 @@ def test_bad_date_parsing(date_s):
         pass
     else:
         assert not config.args.date, "date parsed from {!r}".format(date_s)
+
+def test_ambiguous_arglist_failure():
+    try:
+        # It's ambiguous if "2" is "the 2nd" or "2 EUR".
+        config = config_from(os.devnull, ['historical', '2', 'eur'])
+    except SystemExit:
+        pass
+    else:
+        assert not config.args, "ambiguous args parsed"