diff --git a/.gitignore b/.gitignore
index 77acaadb20..a50ae12c6e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -31,9 +31,6 @@ __pycache__/
 # Local configuration file (sdk path, etc)
 local.properties
 
-# Proguard folder generated by Eclipse
-proguard/
-
 # Log Files
 *.log
 
diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index f2c7d37baa..4293b3bc5f 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -127,24 +127,11 @@ android {
             optimization {
                 enable = true
                 keepRules {
-                    files.add(File(projectDir, "common-proguard-rules.pro"))
-                    files.add(getDefaultProguardFile("proguard-android-optimize.txt"))
-
-                    // Depending on whether the app flavor is enterprise or not we want to use different proguard rules.
-                    val flavorProguardFile = if (isEnterpriseBuild) {
-                        // Custom rules for enterprise builds
-                        File(projectDir, "enterprise-proguard-rules.pro")
-                    } else {
-                        // These default rules prevent the OSS app from being obfuscated
-                        File(projectDir, "default-proguard-rules.pro")
-                    }
-
-                    if (flavorProguardFile.exists()) {
-                        files.add(flavorProguardFile)
-                    } else {
-                        logger.warn("Proguard file ${flavorProguardFile.absolutePath} does not exist")
-                    }
+                    // Equivalent of adding `getDefaultProguardFile("proguard-android-optimize.txt")` (this is the default value).
+                    includeDefault = true
                 }
+                // Our custom keep rules are registered as `keepRules` source folders in the `androidComponents` block below,
+                // as the former `keepRules.files` DSL is deprecated since AGP 9.
             }
         }
 
@@ -229,6 +216,30 @@ androidComponents {
     )
 
     onVariants { variant ->
+        // Register the R8 keep rules source folders for optimized build types (release, nightly).
+        // Replaces the deprecated `optimization.keepRules.files` DSL (AGP 9+).
+        if (variant.buildType != "debug") {
+            variant.sources.keepRules?.let { keepRules ->
+                // Common rules, always applied.
+                keepRules.addStaticSourceDirectory("proguard/common")
+
+                // Depending on whether the app flavor is enterprise or not we want to use different proguard rules.
+                val flavorProguardDir = if (isEnterpriseBuild) {
+                    // Custom rules for enterprise builds
+                    "../enterprise/proguard"
+                } else {
+                    // Custom fules for FOSS builds
+                    "proguard/foss"
+                }
+
+                if (File(projectDir, flavorProguardDir).exists()) {
+                    keepRules.addStaticSourceDirectory(flavorProguardDir)
+                } else {
+                    logger.warn("Proguard folder ${File(projectDir, flavorProguardDir).absolutePath} does not exist")
+                }
+            }
+        }
+
         // Assigns a different version code for each output APK
         // other than the universal APK.
         variant.outputs.forEach { output ->
diff --git a/app/common-proguard-rules.pro b/app/proguard/common/common-proguard-rules.keep
similarity index 100%
rename from app/common-proguard-rules.pro
rename to app/proguard/common/common-proguard-rules.keep
diff --git a/app/default-proguard-rules.pro b/app/proguard/foss/default-proguard-rules.keep
similarity index 100%
rename from app/default-proguard-rules.pro
rename to app/proguard/foss/default-proguard-rules.keep
diff --git a/build.gradle.kts b/build.gradle.kts
index 0e0df9dbc6..6bbc568c66 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -98,7 +98,7 @@ allprojects {
             // This is disabled by default, but the CI will enforce this.
             // You can override by passing `-PallWarningsAsErrors=true` in the command line
             // Or add a line with "allWarningsAsErrors=true" in your ~/.gradle/gradle.properties file
-            allWarningsAsErrors = project.properties["allWarningsAsErrors"] == "true"
+            allWarningsAsErrors = findProperty("allWarningsAsErrors") == "true"
 
             // Uncomment to suppress Compose Kotlin compiler compatibility warning
 //            freeCompilerArgs.addAll(listOf("-P", "plugin:androidx.compose.compiler.plugins.kotlin:suppressKotlinVersionCompatibilityCheck=true"))