diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 41d69ac4..5b8ffa8b 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -6,7 +6,7 @@
 image: node:lts
 
 stages:
-    - test
+    - check
     - build
     - prepare-release
     - release
@@ -17,7 +17,7 @@ cache: &global_cache
         - .yarn/cache
 
 lint:
-    stage: test
+    stage: check
     before_script:
         - yarn install --immutable
     script:
@@ -25,8 +25,17 @@ lint:
     cache:
         <<: *global_cache
 
+typecheck:
+    stage: check
+    before_script:
+        - yarn install --immutable
+    script:
+        - yarn typecheck
+    cache:
+        <<: *global_cache
+
 test:
-    stage: test
+    stage: check
     before_script:
         - yarn install --immutable
     script:
@@ -40,7 +49,7 @@ test:
                 - junit.xml
 
 reuse:
-    stage: test
+    stage: check
     image:
         name: fsfe/reuse:latest
         entrypoint: [""]
diff --git a/src/item/type-specific-helpers/spell.ts b/src/item/type-specific-helpers/spell.ts
index e8820b43..5af27f20 100644
--- a/src/item/type-specific-helpers/spell.ts
+++ b/src/item/type-specific-helpers/spell.ts
@@ -19,21 +19,22 @@ export function calculateSpellPrice(data: DS4SpellDataSourceData): number | null
 function calculateSpellPriceFactor(temporalData: UnitData<TemporalUnit>): number {
     let days: number;
     if (Number.isNumeric(temporalData.value)) {
+        const value = Number.fromString(temporalData.value);
         switch (temporalData.unit) {
             case "days": {
-                days = temporalData.value;
+                days = value;
                 break;
             }
             case "hours": {
-                days = temporalData.value / hoursPerDay;
+                days = value / hoursPerDay;
                 break;
             }
             case "minutes": {
-                days = temporalData.value / (hoursPerDay * minutesPerHour);
+                days = value / (hoursPerDay * minutesPerHour);
                 break;
             }
             case "rounds": {
-                days = (temporalData.value * secondsPerRound) / (hoursPerDay * minutesPerHour * secondsPerMinute);
+                days = (value * secondsPerRound) / (hoursPerDay * minutesPerHour * secondsPerMinute);
                 break;
             }
         }