diff --git a/mobile/android/gradle/with_gecko_binaries.gradle b/mobile/android/gradle/with_gecko_binaries.gradle
index ec1f9e6b908b..27fd71877f56 100644
--- a/mobile/android/gradle/with_gecko_binaries.gradle
+++ b/mobile/android/gradle/with_gecko_binaries.gradle
@@ -7,11 +7,39 @@
 evaluationDependsOn(':annotations')
 
 import groovy.util.FileNameFinder
+import groovy.transform.Memoized
 
 import java.nio.file.Path
 import java.nio.file.Paths
 import java.security.MessageDigest
 
+// To find the LLVM tools from the Android NDK, there are a few wrinkles.  In a compiled build,
+// we can use our own `ANDROID_NDK` configure option.  But in an artifact build, that isn't
+// defined, so we fall back to `android.ndkDirectory` -- but that's defined in
+// `local.properties`, which may not define it.  In that case, fall back to crawling the
+// filesystem.
+@Memoized
+def getNDKDirectory() {
+    if (project.mozconfig.substs.ANDROID_NDK) {
+        return project.mozconfig.substs.ANDROID_NDK
+    }
+    if (project.android.ndkDirectory) {
+        return project.android.ndkDirectory
+    }
+    def mozbuild = System.getenv('MOZBUILD_STATE_PATH') ?: "${System.getProperty('user.home')}/.mozbuild"
+    def files = new FileNameFinder().getFileNames(mozbuild, "android-ndk-*/source.properties")
+    if (files) {
+        // It would be nice to sort these by version, but that's too much effort right now.
+        return project.file(files.first()).parentFile.toString()
+    }
+    return null
+}
+
+ext.getNDKDirectory = {
+    // This is the easiest way to expose the memoized function to consumers.
+    getNDKDirectory()
+}
+
 // Bug 1657190: This task works around a bug in the Android-Gradle plugin.  When using SNAPSHOT
 // builds (and possibly in other situations) the JNI library invalidation process isn't correct.  If
 // there are two JNI libs `a.so` and `b.so` and a new snapshot updates only `a.so`, then the
@@ -26,7 +54,7 @@ import java.security.MessageDigest
 // and use this as our own Mozilla-specific "library generation ID".  We then add our own
 // Mozilla-specific ELF section to every library so that they will all be invalidated by the
 // Android-Gradle plugin of a consuming project.
-class SyncLibsAndUpdateGeneration extends DefaultTask {
+class SyncLibsAndUpdateGenerationID extends DefaultTask {
     @InputDirectory
     File source
 
@@ -36,34 +64,12 @@ class SyncLibsAndUpdateGeneration extends DefaultTask {
     @OutputDirectory
     File destinationDir
 
-    // To find the LLVM tools from the Android NDK, there are a few wrinkles.  In a compiled build,
-    // we can use our own `ANDROID_NDK` configure option.  But in an artifact build, that isn't
-    // defined, so we fall back to `android.ndkDirectory` -- but that's defined in
-    // `local.properties`, which may not define it.  In that case, fall back to crawling the
-    // filesystem.
-    @Input
-    String ndkDirectory = {
-        if (project.mozconfig.substs.ANDROID_NDK) {
-            return project.mozconfig.substs.ANDROID_NDK
-        }
-        if (project.android.ndkDirectory) {
-            return project.android.ndkDirectory
-        }
-        def mozbuild = System.getenv('MOZBUILD_STATE_PATH') ?: "${System.getProperty('user.home')}/.mozbuild"
-        project.logger.lifecycle("mozbuild: ${mozbuild}")
-        def files = new FileNameFinder().getFileNames(mozbuild, "android-ndk-*/source.properties")
-        if (files) {
-            // It would be nice to sort these by version, but that's too much effort right now.
-            return project.file(files.first()).parentFile.toString()
-        }
-        throw new GradleException("Could not determine Android NDK directory.  Set `ndk.dir` in `${project.topsrcdir}/local.properties`")
-    }()
-
     // The `**` in the pattern depends on the host architecture.  We could compute them or bake them
     // in, but this is easy enough.  `FileNameFinder` won't return a directory, so we find a file
     // and return its parent directory.
     @Input
-    File llvmBin = project.file(new FileNameFinder().getFileNames(ndkDirectory, "toolchains/llvm/prebuilt/**/bin/llvm-*").first()).parentFile
+    File llvmBin = project.file(new FileNameFinder().getFileNames(project.ext.getNDKDirectory(), "toolchains/llvm/prebuilt/**/bin/llvm-*")
+                                .first()).parentFile
 
     // Sibling to `.note.gnu.build-id`.
     @Input
@@ -178,12 +184,25 @@ ext.configureVariantWithGeckoBinaries = { variant ->
     }
 
     // For !MOZILLA_OFFICIAL builds, work around an Android-Gradle plugin bug that causes startup
-    // crashes with local substitution.  See class comment above.
-    def syncLibsFromDistDir = { if (!mozconfig.substs.MOZILLA_OFFICIAL) {
+    // crashes with local substitution.  But -- we want to allow artifact builds that don't have the
+    // NDK installed.  See class comment above.
+    def shouldUpdateGenerationID = {
+        if (mozconfig.substs.MOZILLA_OFFICIAL) {
+            return false
+        } else if (ext.getNDKDirectory() == null) {
+            logger.warn("Could not determine Android NDK directory.")
+            logger.warn("Set `ndk.dir` in `${project.topsrcdir}/local.properties` to avoid startup crashes when using `substitute-local-geckoview.gradle`.")
+            logger.warn("See https://bugzilla.mozilla.org/show_bug.cgi?id=1657190.")
+            return false
+        }
+        return true
+    }()
+
+    def syncLibsFromDistDir = { if (shouldUpdateGenerationID) {
         def jarTask = tasks["bundleLibRuntime${variant.name.capitalize()}"]
         def bundleJar = jarTask.outputs.files.find({ it.name == 'classes.jar' })
 
-        task("syncLibsFromDistDirFor${variant.name.capitalize()}", type: SyncLibsAndUpdateGeneration) {
+        task("syncLibsAndUpdateGenerationIDFromDistDirFor${variant.name.capitalize()}", type: SyncLibsAndUpdateGenerationID) {
             source file("${distDir}/lib")
             destinationDir file("${project.buildDir}/moz.build/src/${variant.name}/jniLibs")
             // Include the hash of classes.jar as well, so that JVM-only changes don't leave every