diff --git a/zapcore/increase_level_test.go b/zapcore/increase_level_test.go
index 29fca418e..66892c10f 100644
--- a/zapcore/increase_level_test.go
+++ b/zapcore/increase_level_test.go
@@ -102,11 +102,15 @@ func TestIncreaseLevel(t *testing.T) {
 				if l >= tt.increaseLevel {
 					assert.True(t, enabled, "expect %v to be enabled", l)
 					assert.NotNil(t, ce, "expect non-nil Check")
+					ce.Write()
 				} else {
 					assert.False(t, enabled, "expect %v to be disabled", l)
 					assert.Nil(t, ce, "expect nil Check")
 				}
 			}
+
+			// Verify Sync method doesn't fail.
+			require.NoError(t, filteredLogger.Sync())
 		})
 	}
 }