diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index d47cdd8..704b884 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -6,7 +6,8 @@ on:
   workflow_dispatch:     # Allows manual trigger
 
 env:
-  GOOGLE_OAUTH_CLIENT_ID: ${{ secrets.GOOGLE_OAUTH_CLIENT_ID }}
+  GOOGLE_OAUTH_CLIENT_ID_ANDROID: ${{ secrets.GOOGLE_OAUTH_CLIENT_ID_ANDROID }}
+  GOOGLE_OAUTH_CLIENT_ID_IOS: ${{ secrets.GOOGLE_OAUTH_CLIENT_ID_IOS }}
   SLACK_BOT_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}
   CI: true
 
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 95f03e4..32685f5 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -14,7 +14,8 @@ concurrency:
   cancel-in-progress: ${{ github.ref != 'refs/heads/develop' }}
 
 env:
-  GOOGLE_OAUTH_CLIENT_ID: ${{ secrets.GOOGLE_OAUTH_CLIENT_ID }}
+  GOOGLE_OAUTH_CLIENT_ID_ANDROID: ${{ secrets.GOOGLE_OAUTH_CLIENT_ID_ANDROID }}
+  GOOGLE_OAUTH_CLIENT_ID_IOS: ${{ secrets.GOOGLE_OAUTH_CLIENT_ID_IOS }}
   SLACK_BOT_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}
   # iOS signing (App Store Connect API key) + Firebase App Distribution + match
   APP_STORE_CONNECT_ISSUER_ID: ${{ secrets.APP_STORE_CONNECT_ISSUER_ID }}
diff --git a/common/build.gradle.kts b/common/build.gradle.kts
index 57a03f2..d23cc2e 100644
--- a/common/build.gradle.kts
+++ b/common/build.gradle.kts
@@ -25,7 +25,12 @@ val secretProps = Properties().apply {
 fun secret(key: String, default: String): String =
     secretProps.getProperty(key) ?: project.findProperty(key)?.toString() ?: System.getenv(key) ?: default
 
-val oauthClientId = secret("GOOGLE_OAUTH_CLIENT_ID", "YOUR_OAUTH_CLIENT_ID.apps.googleusercontent.com")
+// Native OAuth clients are per-platform (separate Google Cloud client ids for Android & iOS).
+val oauthClientIdAndroid = secret(
+    "GOOGLE_OAUTH_CLIENT_ID_ANDROID",
+    "YOUR_ANDROID_OAUTH_CLIENT_ID.apps.googleusercontent.com"
+)
+val oauthClientIdIos = secret("GOOGLE_OAUTH_CLIENT_ID_IOS", "YOUR_IOS_OAUTH_CLIENT_ID.apps.googleusercontent.com")
 // endregion
 
 kotlin {
@@ -111,9 +116,26 @@ buildkonfig {
     packageName = "${ProjectSettings.PROJECT_ID}.config"
 
     defaultConfigs {
-        buildConfigField(STRING, "GOOGLE_OAUTH_CLIENT_ID", oauthClientId)
+        // Fallback (Android client id); overridden per target below so shared code can keep
+        // referencing BuildKonfig.GOOGLE_OAUTH_CLIENT_ID and get the platform-correct value.
+        buildConfigField(STRING, "GOOGLE_OAUTH_CLIENT_ID", oauthClientIdAndroid)
         buildConfigField(STRING, "OAUTH_REDIRECT_SCHEME", ProjectSettings.PROJECT_ID)
     }
+
+    targetConfigs {
+        create("android") {
+            buildConfigField(STRING, "GOOGLE_OAUTH_CLIENT_ID", oauthClientIdAndroid)
+        }
+        create("iosX64") {
+            buildConfigField(STRING, "GOOGLE_OAUTH_CLIENT_ID", oauthClientIdIos)
+        }
+        create("iosArm64") {
+            buildConfigField(STRING, "GOOGLE_OAUTH_CLIENT_ID", oauthClientIdIos)
+        }
+        create("iosSimulatorArm64") {
+            buildConfigField(STRING, "GOOGLE_OAUTH_CLIENT_ID", oauthClientIdIos)
+        }
+    }
 }
 
 dependencies {