-

diff --git a/src/core/simulation/simulation.rs b/src/core/simulation/simulation.rs
index 414411e..3384367 100644
--- a/src/core/simulation/simulation.rs
+++ b/src/core/simulation/simulation.rs
@@ -63,7 +63,7 @@ impl<'a> Simulation<'a> {
                     }
                 }
                 InputChange::Money(amount) => {
-                    *state.resources.get_mut(&Resource::Money).unwrap() += amount;
+                    state.subtract_resources(&vec![(Resource::Money, *amount)]);
                 }
                 InputChange::UIMessage(UIMessage::Personnel(action)) => match action {
                     UIPersonnelAction::Hired(bldg_code, role_id, new_person) => {
diff --git a/src/core/simulation/state/state.rs b/src/core/simulation/state/state.rs
index 126728c..8322670 100644
--- a/src/core/simulation/state/state.rs
+++ b/src/core/simulation/state/state.rs
@@ -2,9 +2,12 @@ use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 
 use super::gen::gen_persons;
-use super::models::{BuildingInstance, UnderConstruction, Person};
+use super::models::{BuildingInstance, Person, UnderConstruction};
 
-use crate::data::{schemas::{BuildingType, Resource}, SeedData};
+use crate::data::{
+    schemas::{BuildingType, Resource},
+    SeedData,
+};
 use crate::error::Error;
 use crate::ui::UIMessage;
 
@@ -48,7 +51,7 @@ pub struct State {
     pub resources: HashMap<Resource, i64>,
     pub buildings: Vec<BuildingInstance>,
     pub under_construction: Vec<UnderConstruction>,
-    pub persons: HashMap<String, Person>
+    pub persons: HashMap<String, Person>,
 }
 
 impl State {
@@ -69,14 +72,14 @@ impl State {
         })
     }
 
-    fn subtract_resources(&mut self, costs: HashMap<Resource, i64>) -> Result<(), StateError> {
+    pub fn subtract_resources(&mut self, costs: &[(Resource, i64)]) -> Result<(), StateError> {
         let mut not_met = Vec::new();
         for (res, cost) in costs {
             let available = self.resources[&res];
-            if available >= cost {
-                self.resources.insert(res, available - cost);
+            if available >= *cost {
+                self.resources.insert(*res, available - cost);
             } else {
-                not_met.push(res);
+                not_met.push(*res);
             }
         }
 
@@ -115,7 +118,9 @@ impl State {
     pub fn enqueue_building(&mut self, bldg_type: &BuildingType) -> Result<(), StateError> {
         let (id, build_time, costs) = bldg_type.as_construction_tuple();
 
-        if let Err(e) = self.subtract_resources(costs) {
+        if let Err(e) =
+            self.subtract_resources(&costs.iter().map(|(r, c)| (*r, *c)).collect::<Vec<(_, _)>>())
+        {
             Err(e)
         } else {
             self.under_construction
diff --git a/src/data/schemas.rs b/src/data/schemas.rs
index aa1c77c..4f73fe5 100644
--- a/src/data/schemas.rs
+++ b/src/data/schemas.rs
@@ -3,7 +3,7 @@ use std::collections::HashMap;
 
 use crate::ui::dialogs::{ExperimentPersonnelDialog, PersonHireDialog};
 
-#[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq, Hash)]
+#[derive(Debug, Serialize, Deserialize, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum Resource {
     Research,
     Money,