diff --git a/src/thingdef/thingdef_expression.cpp b/src/thingdef/thingdef_expression.cpp
index 61660ffa8f..00c4b1e752 100644
--- a/src/thingdef/thingdef_expression.cpp
+++ b/src/thingdef/thingdef_expression.cpp
@@ -3593,6 +3593,7 @@ ExpEmit FxArrayElement::Emit(VMFunctionBuilder *build)
 	if (index->isConstant())
 	{
 		unsigned indexval = static_cast<FxConstant *>(index)->GetValue().GetInt();
+		assert(indexval < arraytype->ElementCount && "Array index out of bounds");
 		indexval *= arraytype->ElementSize;
 
 		if (AddressRequested)