diff --git a/tests/datetime/datetimetest.cpp b/tests/datetime/datetimetest.cpp
index 15f17e856b..ff10973ea7 100644
--- a/tests/datetime/datetimetest.cpp
+++ b/tests/datetime/datetimetest.cpp
@@ -822,7 +822,7 @@ void DateTimeTestCase::TestTimeFormat()
         }
     }
 
-    CPPUNIT_ASSERT(wxDateTime::Now().Format("%") == "%");
+    CPPUNIT_ASSERT(wxDateTime::Now().Format("%%") == "%");
 
     wxDateTime dt;