diff --git a/src/faebryk/libs/app/erc.py b/src/faebryk/libs/app/erc.py
index dc52a3de..4bc32803 100644
--- a/src/faebryk/libs/app/erc.py
+++ b/src/faebryk/libs/app/erc.py
@@ -9,6 +9,7 @@
 from faebryk.core.graphinterface import Graph
 from faebryk.core.module import Module
 from faebryk.core.moduleinterface import ModuleInterface
+from faebryk.library.Operation import Operation
 from faebryk.libs.picker.picker import has_part_picked
 from faebryk.libs.util import groupby, print_stack
 
@@ -35,6 +36,11 @@ def __init__(self, faulting_ifs: Sequence[ModuleInterface], *args: object) -> No
         print(stack)
 
 
+class ERCFaultElectricPowerUndefinedVoltage(ERCFault):
+    def __init__(self, faulting_EP: F.ElectricPower, *args: object) -> None:
+        super().__init__([faulting_EP], *args)
+
+
 def simple_erc(G: Graph):
     """Simple ERC check.
 
@@ -54,12 +60,17 @@ def simple_erc(G: Graph):
     """
     logger.info("Checking graph for ERC violations")
 
-    # power short
+    # power short and power with undefined voltage
     electricpower = G.nodes_of_type(F.ElectricPower)
     logger.info(f"Checking {len(electricpower)} Power")
     for ep in electricpower:
         if ep.lv.is_connected_to(ep.hv):
             raise ERCFaultShort([ep], "shorted power")
+        if isinstance(ep.voltage.get_most_narrow(), (F.TBD, Operation)):
+            raise ERCFaultElectricPowerUndefinedVoltage(
+                ep,
+                f"ElectricPower with undefined or unsolved voltage: {ep.voltage}",
+            )
 
     # shorted nets
     nets = G.nodes_of_type(F.Net)