diff --git a/src/main/java/net/neoforged/moddevgradle/internal/PrepareRunOrTest.java b/src/main/java/net/neoforged/moddevgradle/internal/PrepareRunOrTest.java
index 4270cb73..d446a364 100644
--- a/src/main/java/net/neoforged/moddevgradle/internal/PrepareRunOrTest.java
+++ b/src/main/java/net/neoforged/moddevgradle/internal/PrepareRunOrTest.java
@@ -15,6 +15,7 @@
 import net.neoforged.moddevgradle.internal.utils.OperatingSystem;
 import net.neoforged.moddevgradle.internal.utils.StringUtils;
 import net.neoforged.moddevgradle.internal.utils.VersionCapabilitiesInternal;
+import net.neoforged.nfrtgradle.DownloadedAssetsReference;
 import org.gradle.api.DefaultTask;
 import org.gradle.api.GradleException;
 import org.gradle.api.file.ConfigurableFileCollection;
@@ -274,7 +275,7 @@ private void writeProgramArguments(UserDevRunType runConfig, @Nullable String ma
         }
 
         lines.add("# NeoForge Run-Type Program Arguments");
-        var assetProperties = RunUtils.loadAssetProperties(getAssetProperties().get().getAsFile());
+        var assetProperties = DownloadedAssetsReference.loadProperties(getAssetProperties().get().getAsFile());
         List<String> args = runConfig.args();
         for (String arg : args) {
             switch (arg) {
diff --git a/src/main/java/net/neoforged/moddevgradle/internal/RunUtils.java b/src/main/java/net/neoforged/moddevgradle/internal/RunUtils.java
index a7e46922..5771ead4 100644
--- a/src/main/java/net/neoforged/moddevgradle/internal/RunUtils.java
+++ b/src/main/java/net/neoforged/moddevgradle/internal/RunUtils.java
@@ -1,17 +1,13 @@
 package net.neoforged.moddevgradle.internal;
 
-import java.io.BufferedInputStream;
 import java.io.File;
-import java.io.FileInputStream;
 import java.io.IOException;
-import java.io.UncheckedIOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
-import java.util.Properties;
 import java.util.Set;
 import java.util.function.BiConsumer;
 import java.util.stream.Collectors;
@@ -62,25 +58,6 @@ public static Provider<String> getRequiredType(Project project, RunModel runMode
         }));
     }
 
-    public static AssetProperties loadAssetProperties(File file) {
-        Properties assetProperties = new Properties();
-        try (var input = new BufferedInputStream(new FileInputStream(file))) {
-            assetProperties.load(input);
-        } catch (IOException e) {
-            throw new UncheckedIOException("Failed to load asset properties", e);
-        }
-        if (!assetProperties.containsKey("assets_root")) {
-            throw new IllegalStateException("Asset properties file does not contain assets_root");
-        }
-        if (!assetProperties.containsKey("asset_index")) {
-            throw new IllegalStateException("Asset properties file does not contain asset_index");
-        }
-
-        return new AssetProperties(
-                assetProperties.getProperty("asset_index"),
-                assetProperties.getProperty("assets_root"));
-    }
-
     public static void writeLog4j2Configuration(Level rootLevel, Path destination) throws IOException {
         Files.writeString(destination, """
                 <?xml version="1.0" encoding="UTF-8"?>
@@ -290,8 +267,6 @@ public static Provider<Map<String, ModFolder>> buildModFolders(Project project,
     }
 }
 
-record AssetProperties(String assetIndex, String assetsRoot) {}
-
 abstract class ModFoldersProvider implements CommandLineArgumentProvider {
     @Inject
     public ModFoldersProvider() {
diff --git a/src/main/java/net/neoforged/nfrtgradle/DownloadAssets.java b/src/main/java/net/neoforged/nfrtgradle/DownloadAssets.java
index 49cbf3a3..4d9ab1d6 100644
--- a/src/main/java/net/neoforged/nfrtgradle/DownloadAssets.java
+++ b/src/main/java/net/neoforged/nfrtgradle/DownloadAssets.java
@@ -1,10 +1,13 @@
 package net.neoforged.nfrtgradle;
 
+import java.io.File;
 import java.util.ArrayList;
 import java.util.Collections;
 import javax.inject.Inject;
 import org.gradle.api.GradleException;
+import org.gradle.api.Task;
 import org.gradle.api.file.RegularFileProperty;
+import org.gradle.api.logging.Logger;
 import org.gradle.api.provider.Property;
 import org.gradle.api.tasks.Input;
 import org.gradle.api.tasks.Optional;
@@ -21,7 +24,9 @@
 @ApiStatus.NonExtendable
 public abstract class DownloadAssets extends NeoFormRuntimeTask {
     @Inject
-    public DownloadAssets() {}
+    public DownloadAssets() {
+        getOutputs().upToDateWhen(DownloadAssets::checkAssetValidity);
+    }
 
     /**
      * Gradle dependency notation for the NeoForm data artifact, from which a Minecraft version will be derived.
@@ -109,4 +114,37 @@ public void downloadAssets() {
 
         run(args);
     }
+
+    private static boolean checkAssetValidity(Task task) {
+        var downloadTask = (DownloadAssets) task;
+        var logger = downloadTask.getLogger();
+
+        var assetReferenceFile = downloadTask.getAssetPropertiesFile();
+        if (assetReferenceFile.isPresent()) {
+            DownloadedAssetsReference assetReference;
+            try {
+                assetReference = DownloadedAssetsReference.loadProperties(assetReferenceFile.getAsFile().get());
+            } catch (Exception e) {
+                logger.error("Failed to read downloaded asset index: {}", assetReferenceFile);
+                return false;
+            }
+            return validateAssetReference(assetReference, logger);
+        }
+
+        return true;
+    }
+
+    private static boolean validateAssetReference(DownloadedAssetsReference assetReference, Logger logger) {
+        File assetRoot = new File(assetReference.assetsRoot());
+        if (!assetRoot.isDirectory()) {
+            logger.info("Downloaded assets directory has gone missing: {}", assetRoot);
+            return false;
+        }
+        File assetIndex = new File(assetRoot, "indexes/" + assetReference.assetIndex() + ".json");
+        if (!assetIndex.isFile()) {
+            logger.info("Downloaded assets index has gone missing: {}", assetIndex);
+            return false;
+        }
+        return true;
+    }
 }
diff --git a/src/main/java/net/neoforged/nfrtgradle/DownloadedAssetsReference.java b/src/main/java/net/neoforged/nfrtgradle/DownloadedAssetsReference.java
new file mode 100644
index 00000000..6c6f165a
--- /dev/null
+++ b/src/main/java/net/neoforged/nfrtgradle/DownloadedAssetsReference.java
@@ -0,0 +1,29 @@
+package net.neoforged.nfrtgradle;
+
+import java.io.BufferedInputStream;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.util.Properties;
+
+public record DownloadedAssetsReference(String assetIndex, String assetsRoot) {
+    public static DownloadedAssetsReference loadProperties(File file) {
+        Properties assetProperties = new Properties();
+        try (var input = new BufferedInputStream(new FileInputStream(file))) {
+            assetProperties.load(input);
+        } catch (IOException e) {
+            throw new UncheckedIOException("Failed to load asset properties", e);
+        }
+        if (!assetProperties.containsKey("assets_root")) {
+            throw new IllegalStateException("Asset properties file does not contain assets_root");
+        }
+        if (!assetProperties.containsKey("asset_index")) {
+            throw new IllegalStateException("Asset properties file does not contain asset_index");
+        }
+
+        return new DownloadedAssetsReference(
+                assetProperties.getProperty("asset_index"),
+                assetProperties.getProperty("assets_root"));
+    }
+}