diff --git a/app/build.gradle b/app/build.gradle
index eedf821b..b3c8c8aa 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -82,7 +82,7 @@ dependencies {
     implementation project(':vcard4android')
 
     implementation 'androidx.multidex:multidex:2.0.1'
-    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:${versions.kotlin}"
 
     implementation 'androidx.appcompat:appcompat:1.0.2'
     implementation 'androidx.cardview:cardview:1.0.0'
diff --git a/build.gradle b/build.gradle
index 3962a6e5..dc3834ec 100644
--- a/build.gradle
+++ b/build.gradle
@@ -7,17 +7,19 @@
  */
 
 buildscript {
-    ext.dokka_version = '0.9.17'
-    ext.kotlin_version = '1.3.21'
+    ext.versions = [
+        kotlin: '1.3.30',
+        dokka: '0.9.17'
+    ]
 
     repositories {
         jcenter()
         google()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.3.2'
-        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
-        classpath "org.jetbrains.dokka:dokka-android-gradle-plugin:$dokka_version"
+        classpath 'com.android.tools.build:gradle:3.4.0'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:${versions.kotlin}"
+        classpath "org.jetbrains.dokka:dokka-android-gradle-plugin:${versions.dokka}"
     }
 }
 
diff --git a/cert4android b/cert4android
index b1f57b51..aae988de 160000
--- a/cert4android
+++ b/cert4android
@@ -1 +1 @@
-Subproject commit b1f57b518f7595eabf9842d0b950cdc82f0e21db
+Subproject commit aae988de2107873e2130b175969ce9b49e8fc0b6
diff --git a/dav4jvm b/dav4jvm
index f141bd62..3866bb27 160000
--- a/dav4jvm
+++ b/dav4jvm
@@ -1 +1 @@
-Subproject commit f141bd620f58155231b6b45a38e8e29212a5165e
+Subproject commit 3866bb2725cae131d3490f2692bc15b9e1396bc8
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index dd43e0d0..bf1e4648 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -1,6 +1,6 @@
-#Thu Mar 29 12:34:22 CEST 2018
+#Wed Apr 17 22:31:47 CEST 2019
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-5.1-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-5.1.1-all.zip
diff --git a/ical4android b/ical4android
index 94feded0..8f201fbf 160000
--- a/ical4android
+++ b/ical4android
@@ -1 +1 @@
-Subproject commit 94feded02e00b3b58645cf1b7af187ade718bf9e
+Subproject commit 8f201fbfb05d26d4180365dc493ee53c436291da
diff --git a/vcard4android b/vcard4android
index 4e5acd17..f5498aff 160000
--- a/vcard4android
+++ b/vcard4android
@@ -1 +1 @@
-Subproject commit 4e5acd17221491006014affb33cb5f41b8b84ed9
+Subproject commit f5498aff6746e0cc089c9c99e430cf483e4fa9d0