diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 2b3e35ba4..cbc6dc61c 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -8,6 +8,8 @@ cache:
 variables:
   AVD_SDK: "17"
   SKIN: "QVGA"
+  # switch glibc to a memory conserving mode
+  MALLOC_ARENA_MAX: "2"
 
 gradle:
   script:
@@ -17,9 +19,9 @@ gradle:
     # always report on lint errors to the build log
     - sed -i -e 's,textReport .*,textReport true,' app/build.gradle
     # 'build' means assemble and check
-    - ./gradlew build || {
+    - ./gradlew build -PdisablePreDex || {
           for log in app/build/reports/*ests/*/*ml; do
-              echo "read $log here:"
+              echo "read $log here:";
               cat "$log" | curl --silent -F 'clbin=<-' https://clbin.com;
           done;
           exit 1;
@@ -38,9 +40,9 @@ gradle:
         --target android-$AVD_SDK
     - emulator64-arm -avd fcl-test -no-skin -no-audio -no-window &
     - ./tools/wait-for-emulator
-    - adb shell input keyevent 82
+    - adb shell input keyevent 82 &
     - export EXITVALUE=0
-    - ADB_INSTALL_TIMEOUT=8 ./gradlew connectedCheck || {
+    - ADB_INSTALL_TIMEOUT=8 ./gradlew connectedCheck -PdisablePreDex || {
         adb -e logcat -d '*:E';
         echo "get the full logcat here:";
         adb -e logcat -d | curl --silent -F 'clbin=<-' https://clbin.com;
@@ -52,17 +54,19 @@ gradle:
         cat "$log" | curl --silent -F 'clbin=<-' https://clbin.com;
       done
     - sed -n 's/.*"ctr2">\([0-9]*\)%<.*/Coverage - \1.0% covered\n/p' app/build/reports/coverage/debug/index.html
+    # this file changes every time but should not be cached
+    - rm -f $GRADLE_USER_HOME/caches/modules-2/modules-2.lock
     - exit $EXITVALUE
 
 pmd:
   script:
     - export GRADLE_USER_HOME=$PWD/.gradle
-    - ./gradlew pmd
+    - ./gradlew pmd -PdisablePreDex
 
 checkstyle:
   script:
     - export GRADLE_USER_HOME=$PWD/.gradle
-    - ./gradlew checkstyle
+    - ./gradlew checkstyle -PdisablePreDex
 
 tools:
   script:
diff --git a/app/build.gradle b/app/build.gradle
index 5103af08b..e5967b14b 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -157,8 +157,17 @@ android {
     }
 
     testOptions {
-        // prevent tests from dying on android.util.Log calls
-        unitTests.returnDefaultValues = true
+        unitTests {
+            // prevent tests from dying on android.util.Log calls
+            returnDefaultValues = true
+            all {
+                // All the usual Gradle options.
+                testLogging {
+                    events "skipped", "failed", "standardOut", "standardError"
+                    showStandardStreams = true
+                }
+            }
+        }
     }
 
     lintOptions {
diff --git a/app/src/test/java/org/fdroid/fdroid/net/HttpDownloaderTest.java b/app/src/test/java/org/fdroid/fdroid/net/HttpDownloaderTest.java
index 9d92fa74e..7b56bee6b 100644
--- a/app/src/test/java/org/fdroid/fdroid/net/HttpDownloaderTest.java
+++ b/app/src/test/java/org/fdroid/fdroid/net/HttpDownloaderTest.java
@@ -16,13 +16,11 @@ import static org.junit.Assert.fail;
 public class HttpDownloaderTest {
 
     String[] urls = {
-            "https://www.google.com",
             "https://en.wikipedia.org/wiki/Index.html",
             "https://mirrors.kernel.org/debian/dists/stable/Release",
-            "https://f-droid.org/archive/de.we.acaldav_5.apk",
+            "https://f-droid.org/repo/index.jar",
             // sites that use SNI for HTTPS
             "https://guardianproject.info/fdroid/repo/index.jar",
-            "https://firstlook.org",
     };
 
     private boolean receivedProgress;
@@ -42,23 +40,38 @@ public class HttpDownloaderTest {
 
     @Test
     public void downloadUninterruptedTestWithProgress() throws IOException, InterruptedException {
-        for (String urlString : urls) {
-            receivedProgress = false;
-            URL url = new URL(urlString);
-            File destFile = File.createTempFile("dl-", "");
-            HttpDownloader httpDownloader = new HttpDownloader(url, destFile);
-            httpDownloader.setListener(new Downloader.DownloaderProgressListener() {
-                @Override
-                public void sendProgress(URL sourceUrl, int bytesRead, int totalBytes) {
-                    receivedProgress = true;
+        final CountDownLatch latch = new CountDownLatch(1);
+        String urlString = "https://f-droid.org/repo/index.jar";
+        receivedProgress = false;
+        System.out.println("downloadUninterruptedTestWithProgress: " + urlString);
+        receivedProgress = false;
+        URL url = new URL(urlString);
+        File destFile = File.createTempFile("dl-", "");
+        final HttpDownloader httpDownloader = new HttpDownloader(url, destFile);
+        httpDownloader.setListener(new Downloader.DownloaderProgressListener() {
+            @Override
+            public void sendProgress(URL sourceUrl, int bytesRead, int totalBytes) {
+                System.out.println("DownloaderProgressListener.sendProgress " + sourceUrl + " " + bytesRead + " / " + totalBytes);
+                receivedProgress = true;
+            }
+        });
+        new Thread() {
+            @Override
+            public void run() {
+                try {
+                    httpDownloader.download();
+                    latch.countDown();
+                } catch (IOException | InterruptedException e) {
+                    e.printStackTrace();
+                    fail();
                 }
-            });
-            httpDownloader.download();
-            assertTrue(destFile.exists());
-            assertTrue(destFile.canRead());
-            assertTrue(receivedProgress);
-            destFile.deleteOnExit();
-        }
+            }
+        }.start();
+        latch.await(100, TimeUnit.SECONDS); // either 2 progress reports or 100 seconds
+        assertTrue(destFile.exists());
+        assertTrue(destFile.canRead());
+        assertTrue(receivedProgress);
+        destFile.deleteOnExit();
     }
 
     @Test
diff --git a/build.gradle b/build.gradle
index e02ad215c..2b3560d32 100644
--- a/build.gradle
+++ b/build.gradle
@@ -7,3 +7,19 @@ buildscript {
         classpath files('libs/gradle-witness.jar')
     }
 }
+
+/**
+ * Improve build server performance by allowing disabling of pre-dexing
+ * (see http://tools.android.com/tech-docs/new-build-system/tips#TOC-Improving-Build-Server-performance.)
+ */
+project.ext.preDexLibs = !project.hasProperty('disablePreDex')
+
+subprojects {
+  project.plugins.whenPluginAdded { plugin ->
+    if ("com.android.build.gradle.AppPlugin".equals(plugin.class.name)) {
+      project.android.dexOptions.preDexLibraries = rootProject.ext.preDexLibs
+    } else if ("com.android.build.gradle.LibraryPlugin".equals(plugin.class.name)) {
+      project.android.dexOptions.preDexLibraries = rootProject.ext.preDexLibs
+    }
+  }
+}