diff --git a/schedule/__init__.py b/schedule/__init__.py
index 8e12eeb7..7d8b745b 100644
--- a/schedule/__init__.py
+++ b/schedule/__init__.py
@@ -302,7 +302,7 @@ def is_repr(j):
         if self.at_time is not None:
             return "Every %s %s at %s do %s %s" % (
                 self.interval,
-                self.unit[:-1] if self.interval == 1 else self.unit,
+                self.unit[:-1] if self.interval == 1 and self.unit else self.unit,
                 self.at_time,
                 call_repr,
                 timestats,
@@ -317,7 +317,7 @@ def is_repr(j):
             return fmt % dict(
                 interval=self.interval,
                 latest=self.latest,
-                unit=(self.unit[:-1] if self.interval == 1 else self.unit),
+                unit=(self.unit[:-1] if self.interval == 1 and self.unit else self.unit),
                 call_repr=call_repr,
                 timestats=timestats,
             )