diff --git a/apps/openmw/mwclass/npc.cpp b/apps/openmw/mwclass/npc.cpp
index 6506b13b4c..b9e03aa45c 100644
--- a/apps/openmw/mwclass/npc.cpp
+++ b/apps/openmw/mwclass/npc.cpp
@@ -94,7 +94,7 @@ namespace
         for (const ESM::Attribute& attribute : attributes)
         {
             const ESM::Race::MaleFemale& value
-                = race->mData.mAttributeValues[ESM::Attribute::refIdToIndex(attribute.mId)];
+                = race->mData.mAttributeValues[static_cast<size_t>(ESM::Attribute::refIdToIndex(attribute.mId))];
             creatureStats.setAttribute(attribute.mId, male ? value.mMale : value.mFemale);
         }
 
diff --git a/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp b/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp
index 29fe4dd2a6..ff720345bc 100644
--- a/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp
+++ b/apps/openmw/mwmechanics/mechanicsmanagerimp.cpp
@@ -151,7 +151,7 @@ namespace MWMechanics
             for (const ESM::Attribute& attribute : esmStore.get<ESM::Attribute>())
             {
                 const ESM::Race::MaleFemale& value
-                    = race->mData.mAttributeValues[ESM::Attribute::refIdToIndex(attribute.mId)];
+                    = race->mData.mAttributeValues[static_cast<size_t>(ESM::Attribute::refIdToIndex(attribute.mId))];
 
                 creatureStats.setAttribute(attribute.mId, male ? value.mMale : value.mFemale);
             }
diff --git a/apps/openmw/mwmechanics/npcstats.cpp b/apps/openmw/mwmechanics/npcstats.cpp
index 5c62eb8276..3427e460c3 100644
--- a/apps/openmw/mwmechanics/npcstats.cpp
+++ b/apps/openmw/mwmechanics/npcstats.cpp
@@ -467,7 +467,7 @@ void MWMechanics::NpcStats::writeState(ESM::NpcStats& state) const
         // TODO extend format
         auto index = ESM::Skill::refIdToIndex(id);
         assert(index >= 0);
-        value.writeState(state.mSkills[static_cast<unsigned int>(index)]);
+        value.writeState(state.mSkills[static_cast<size_t>(index)]);
     }
 
     state.mIsWerewolf = mIsWerewolf;
@@ -488,7 +488,7 @@ void MWMechanics::NpcStats::writeState(ESM::NpcStats& state) const
 
     state.mSkillIncrease.fill(0);
     for (const auto& [key, value] : mSkillIncreases)
-        state.mSkillIncrease[ESM::Attribute::refIdToIndex(key)] = value;
+        state.mSkillIncrease[static_cast<size_t>(ESM::Attribute::refIdToIndex(key))] = value;
 
     for (size_t i = 0; i < state.mSpecIncreases.size(); ++i)
         state.mSpecIncreases[i] = mSpecIncreases[i];