diff --git a/labware/liquids.py b/labware/liquids.py
index <HASH>..<HASH> 100644
--- a/labware/liquids.py
+++ b/labware/liquids.py
@@ -73,7 +73,7 @@ class LiquidContainer():
 
 	def assert_capacity(self, new_amount, ml=False):
 		if not self.max_volume:
-			return
+			raise ValueError("No maximum liquid amount set for well.")
 		new_value = self.calculate_total_volume()+new_amount
 		if (new_value > self.max_volume):
 			raise VolumeError(
LiquidContainer: Force maximum limit.

I'm not actually sure why the tests concerning maximum limits on
MicroplateWell are passing. Need to figure out where they're set.