diff --git a/scripts/build-unity-package.ps1 b/scripts/build-unity-package.ps1
index bdd9fff6..3258155f 100644
--- a/scripts/build-unity-package.ps1
+++ b/scripts/build-unity-package.ps1
@@ -128,6 +128,19 @@ $expectedAssemblies = @(
   "System.Text.Json.dll",
   "System.Threading.Channels.dll"
 )
+# Assemblies the package references but never ships: org.gamecult.cultmath owns CultMath.dll, and the
+# package.json dependency delivers it. A second copy in Runtime\Plugins would be a duplicate assembly.
+$externalAssemblies = @("CultMath.dll")
+$asmdef = Get-Content -LiteralPath (Join-Path $templateRoot "Runtime\GameCult.CultLib.asmdef") -Raw | ConvertFrom-Json
+$referencedAssemblies = @($asmdef.precompiledReferences | Sort-Object)
+$declaredAssemblies = @($expectedAssemblies + $externalAssemblies | Sort-Object)
+if (($referencedAssemblies -join "|") -ne ($declaredAssemblies -join "|")) {
+  throw "GameCult.CultLib.asmdef precompiledReferences differ from the shipped plus external assembly lists."
+}
+$cultMathDependency = (Get-Content -LiteralPath (Join-Path $templateRoot "package.json") -Raw | ConvertFrom-Json).dependencies.'org.gamecult.cultmath'
+if ([string]::IsNullOrWhiteSpace($cultMathDependency)) {
+  throw "package.json must declare org.gamecult.cultmath, which supplies CultMath.dll."
+}
 $publishedByName = @{}
 foreach ($assembly in Get-ChildItem -LiteralPath $publishRoot -Filter "*.dll") {
   $publishedByName[$assembly.Name] = $assembly
@@ -154,6 +167,11 @@ foreach ($assemblyName in $expectedAssemblies) {
     Copy-Item -LiteralPath $pdb -Destination $pluginRoot
   }
 }
+foreach ($external in $externalAssemblies) {
+  if (Test-Path -LiteralPath (Join-Path $pluginRoot $external)) {
+    throw "CultLib Unity package must not ship $external; org.gamecult.cultmath owns it."
+  }
+}
 $nativePluginRoot = Join-Path $pluginRoot "x86_64"
 New-Item -ItemType Directory -Force -Path $nativePluginRoot | Out-Null
 Copy-Item -LiteralPath (Join-Path $quicNativeRoot "gamecult_mesh_quic_native.dll") -Destination $nativePluginRoot
diff --git a/unity/org.gamecult.cultlib/README.md b/unity/org.gamecult.cultlib/README.md
index 88a083e1..8716d7e4 100644
--- a/unity/org.gamecult.cultlib/README.md
+++ b/unity/org.gamecult.cultlib/README.md
@@ -17,6 +17,15 @@ Install version `1.0.57` through Unity Package Manager with:
 https://github.com/GameCult/CultLib.git?path=/unity/org.gamecult.cultlib#cultlib-unity-v1.0.57
 ```
 
+The package depends on `org.gamecult.cultmath` (0.3.0 or later) and does not
+carry its own `CultMath.dll`. Unity Package Manager resolves git packages only
+from the project manifest, so add CultMath beside CultLib in
+`Packages/manifest.json`:
+
+```text
+"org.gamecult.cultmath": "https://github.com/GameCult/CultLib.git?path=/packages/cultmath/unity/org.gamecult.cultmath#cultmath-unity-v0.3.0"
+```
+
 CultMesh chooses mapped memory for reachable same-machine bodies and advertised
 QUIC for remote realtime state. Applications register the packaged
 `CultMeshNativeQuicRealtimeTransportConnector`; they do not load or configure
diff --git a/unity/org.gamecult.cultlib/Runtime/GameCult.CultLib.asmdef b/unity/org.gamecult.cultlib/Runtime/GameCult.CultLib.asmdef
index bd13cb38..0ddbb9a6 100644
--- a/unity/org.gamecult.cultlib/Runtime/GameCult.CultLib.asmdef
+++ b/unity/org.gamecult.cultlib/Runtime/GameCult.CultLib.asmdef
@@ -8,6 +8,7 @@
   "overrideReferences": true,
   "precompiledReferences": [
     "ConcurrentCollections.dll",
+    "CultMath.dll",
     "GameCult.Caching.dll",
     "GameCult.Caching.MessagePack.dll",
     "GameCult.Logging.dll",
diff --git a/unity/org.gamecult.cultlib/package.json b/unity/org.gamecult.cultlib/package.json
index 722190cf..6545bed1 100644
--- a/unity/org.gamecult.cultlib/package.json
+++ b/unity/org.gamecult.cultlib/package.json
@@ -3,6 +3,9 @@
   "displayName": "CultLib",
   "version": "1.0.60",
   "unity": "2021.3",
+  "dependencies": {
+    "org.gamecult.cultmath": "0.3.0"
+  },
   "description": "CultCache, CultNet, and CultMesh managed runtime assemblies for Unity.",
   "license": "MIT",
   "author": {