diff --git a/IPython/core/interactiveshell.py b/IPython/core/interactiveshell.py
index 4c1863a..4c8e973 100644
--- a/IPython/core/interactiveshell.py
+++ b/IPython/core/interactiveshell.py
@@ -2125,7 +2125,7 @@ class InteractiveShell(SingletonConfigurable):
                                     'did you mean that instead?)' % magic_name )
             error(etpl % (magic_name, extra))
         elif cell == '':
-            warn('%%%%%s line but no cell' % magic_name)
+            raise UsageError('%%%%%s has line but no cell' % magic_name)
         else:
             # Note: this is the distance in the stack to the user's frame.
             # This will need to be updated if the internal calling logic gets