diff --git a/CHANGELOG.md b/CHANGELOG.md
index 90f55d48..b5469b64 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Added
 - Better troubleshooting for connection problems.
+  [#127](https://github.com/scionproto-contrib/jpan/pull/127)
+- Auto-add port to discovery server setting + better error message.
   [#128](https://github.com/scionproto-contrib/jpan/pull/128)
 
 ### Fixed
diff --git a/README.md b/README.md
index 01b23fb5..fe62749d 100644
--- a/README.md
+++ b/README.md
@@ -415,13 +415,9 @@ If you have a topology file, you can specify it via environment variable `SCION_
 or via Java property `org.scion.bootstrap.topoFile`:
 
 ```java
-System.setProperty(Constants.PROPERTY_BOOTSTRAP_HOST, "youtTopoFile.json");
+System.setProperty(Constants.PROPERTY_BOOTSTRAP_HOST, "yourTopoFile.json");
 ```
 
-
-
-
-
 ### Local testbed (scionproto) does not contain any path
 
 A common problem is that the certificates of the testbed have expired (default validity: 3 days).
diff --git a/src/main/java/org/scion/jpan/internal/ScionBootstrapper.java b/src/main/java/org/scion/jpan/internal/ScionBootstrapper.java
index 6e8448e2..b31002b4 100644
--- a/src/main/java/org/scion/jpan/internal/ScionBootstrapper.java
+++ b/src/main/java/org/scion/jpan/internal/ScionBootstrapper.java
@@ -44,7 +44,7 @@ public class ScionBootstrapper {
   private final GlobalTopology world;
 
   protected ScionBootstrapper(String topologyServiceAddress) {
-    this.topologyResource = topologyServiceAddress;
+    this.topologyResource = IPHelper.ensurePortOrDefault(topologyServiceAddress, 8041);
     this.localAS = initLocal();
     this.world = initGlobal();
   }
@@ -142,7 +142,7 @@ public String fetchFile(String resource) {
       return fetchFile(url);
     } catch (IOException e) {
       throw new ScionRuntimeException(
-          "While fetching resource '" + resource + "' from " + topologyResource);
+          "While fetching resource '" + resource + "' from " + topologyResource, e);
     }
   }
 
diff --git a/src/test/java/org/scion/jpan/api/ScionTest.java b/src/test/java/org/scion/jpan/api/ScionTest.java
index df7f7e7e..cf4287c5 100644
--- a/src/test/java/org/scion/jpan/api/ScionTest.java
+++ b/src/test/java/org/scion/jpan/api/ScionTest.java
@@ -145,14 +145,9 @@ void defaultService_bootstrapAddress() {
 
     MockNetwork.startTiny(MockNetwork.Mode.BOOTSTRAP);
     try {
-      String host;
-      MockBootstrapServer mts = MockNetwork.getTopoServer();
-      if (mts.getAddress().getAddress() instanceof Inet6Address) {
-        host = "[" + mts.getAddress().getAddress().getHostAddress() + "]";
-      } else {
-        host = mts.getAddress().getHostString();
-      }
-      host += ":" + mts.getAddress().getPort();
+      InetSocketAddress discoveryAddress = MockNetwork.getTopoServer().getAddress();
+      String host = ToStringUtil.toString(discoveryAddress.getAddress());
+      host += ":" + discoveryAddress.getPort();
 
       System.setProperty(Constants.PROPERTY_BOOTSTRAP_HOST, host);
       ScionService service = Scion.defaultService();
@@ -164,6 +159,23 @@ void defaultService_bootstrapAddress() {
     }
   }
 
+  @Test
+  void defaultService_bootstrapAddress_defaultPort() {
+    MockNetwork.startTiny(MockNetwork.Mode.BOOTSTRAP);
+    try {
+      InetSocketAddress discoveryAddress = MockNetwork.getTopoServer().getAddress();
+      String host = ToStringUtil.toString(discoveryAddress.getAddress());
+      // We do _not_ add a port here.
+
+      System.setProperty(Constants.PROPERTY_BOOTSTRAP_HOST, host);
+      Throwable t = assertThrows(ScionRuntimeException.class, Scion::defaultService);
+      // Check that the default port 8041 was added
+      assertTrue(t.getMessage().contains(host + ":8041"));
+    } finally {
+      MockNetwork.stopTiny();
+    }
+  }
+
   @Test
   void defaultService_bootstrapNaptrRecord() {
     long dstIA = ScionUtil.parseIA("1-ff00:0:112");
diff --git a/src/test/java/org/scion/jpan/demo/util/ToStringUtil.java b/src/test/java/org/scion/jpan/demo/util/ToStringUtil.java
index 2ca4e777..c9a54e60 100644
--- a/src/test/java/org/scion/jpan/demo/util/ToStringUtil.java
+++ b/src/test/java/org/scion/jpan/demo/util/ToStringUtil.java
@@ -125,4 +125,14 @@ public static String pathLong(byte[] raw) {
     ph.read(ByteBuffer.wrap(raw));
     return ph.toString();
   }
+
+  public static String toString(InetAddress address) {
+    String host;
+    if (address instanceof Inet6Address) {
+      host = "[" + address.getHostAddress() + "]";
+    } else {
+      host = address.toString().substring(1);
+    }
+    return host;
+  }
 }