diff --git a/pom.xml b/pom.xml
index 943a5bf..eb1e21b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -73,11 +73,6 @@
             <version>1.6</version>
             <optional>true</optional>
         </dependency>
-        <dependency>
-            <groupId>com.google.guava</groupId>
-            <artifactId>guava</artifactId>
-            <version>18.0</version>
-        </dependency>
         <dependency>
             <groupId>org.apache.commons</groupId>
             <artifactId>commons-lang3</artifactId>
diff --git a/src/main/java/org/graylog2/syslog4j/impl/message/structured/StructuredSyslogMessage.java b/src/main/java/org/graylog2/syslog4j/impl/message/structured/StructuredSyslogMessage.java
index 1235c48..8960291 100644
--- a/src/main/java/org/graylog2/syslog4j/impl/message/structured/StructuredSyslogMessage.java
+++ b/src/main/java/org/graylog2/syslog4j/impl/message/structured/StructuredSyslogMessage.java
@@ -1,12 +1,12 @@
 package org.graylog2.syslog4j.impl.message.structured;
 
-import com.google.common.base.Preconditions;
-import com.google.common.collect.Maps;
 import org.apache.commons.lang3.StringUtils;
 import org.graylog2.syslog4j.SyslogConstants;
 import org.graylog2.syslog4j.impl.message.AbstractSyslogMessage;
+import org.graylog2.syslog4j.util.Preconditions;
 
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Set;
@@ -121,7 +121,7 @@ public class StructuredSyslogMessage extends AbstractSyslogMessage implements St
             end=stringMessage.indexOf(SyslogConstants.STRUCTURED_DATA_EMPTY_VALUE)+4;
         } else {
 
-            final Map<String, Map<String, String>> structuredDataMap = Maps.newHashMap();
+            final Map<String, Map<String, String>> structuredDataMap = new HashMap<String, Map<String, String>>();
 
             while(start < stringMessage.length() && matchChar(stringMessage, start, '[') == start) {
                 Preconditions.checkArgument(stringMessage.charAt(start) == '[', "Invalid structured data in syslog message '%s'", stringMessage);
@@ -129,7 +129,7 @@ public class StructuredSyslogMessage extends AbstractSyslogMessage implements St
                 Preconditions.checkArgument(end != -1 && stringMessage.charAt(end) == ']', "Invalid structured data in syslog message '%s'", stringMessage);
 
                 String key = null;
-                Map<String, String> keyMap = Maps.newHashMap();
+                Map<String, String> keyMap = new HashMap<String, String>();
                 while (start < end) {
                     if (key == null) {
                         final int keyEnd = matchChar(stringMessage, ++start, ']', ' '); // Key can be terminated by a space (then more fields to follow) or a ]
@@ -138,7 +138,6 @@ public class StructuredSyslogMessage extends AbstractSyslogMessage implements St
                     } else {
                         Preconditions.checkArgument(start < stringMessage.length() && stringMessage.charAt(start) == ' ', "Invalid structured data in syslog message '%s'", stringMessage);
                         start = start + 1; // Start points at the space behind either the key or the previous value
-                        Preconditions.checkArgument(key != null, "Invalid structured data in syslog message '%s'", stringMessage);
                         final int equalsIndex = stringMessage.indexOf('=', start); // Equals terminates the field name.
                         Preconditions.checkArgument(equalsIndex != -1, "Invalid structured data in syslog message '%s'", stringMessage);
                         Preconditions.checkArgument(stringMessage.charAt(equalsIndex + 1) == '"', "Invalid structured data in syslog message '%s'", stringMessage);
diff --git a/src/main/java/org/graylog2/syslog4j/util/Preconditions.java b/src/main/java/org/graylog2/syslog4j/util/Preconditions.java
new file mode 100644
index 0000000..e64fd22
--- /dev/null
+++ b/src/main/java/org/graylog2/syslog4j/util/Preconditions.java
@@ -0,0 +1,26 @@
+package org.graylog2.syslog4j.util;
+
+public final class Preconditions {
+    private Preconditions() {
+    }
+
+    public static void checkArgument(boolean expression) {
+        if (!expression) {
+            throw new IllegalArgumentException();
+        }
+    }
+
+    public static void checkArgument(boolean expression, Object errorMessage) {
+        if (!expression) {
+            throw new IllegalArgumentException(String.valueOf(errorMessage));
+        }
+    }
+
+    public static void checkArgument(boolean expression,
+                                     String errorMessageTemplate,
+                                     Object... errorMessageArgs) {
+        if (!expression) {
+            throw new IllegalArgumentException(String.format(errorMessageTemplate, errorMessageArgs));
+        }
+    }
+}
diff --git a/src/test/java/org/graylog2/syslog4j/test/message/structured/StructuredSyslogMessageTest.java b/src/test/java/org/graylog2/syslog4j/test/message/structured/StructuredSyslogMessageTest.java
index ab4a6e4..5013c68 100644
--- a/src/test/java/org/graylog2/syslog4j/test/message/structured/StructuredSyslogMessageTest.java
+++ b/src/test/java/org/graylog2/syslog4j/test/message/structured/StructuredSyslogMessageTest.java
@@ -48,13 +48,13 @@ package org.graylog2.syslog4j.test.message.structured;
 // Date: Jul 15, 2009
 // ---------------------
 
-import com.google.common.collect.Maps;
 import junit.framework.TestCase;
 import org.graylog2.syslog4j.impl.message.structured.StructuredSyslogMessage;
 import org.graylog2.syslog4j.server.impl.event.structured.StructuredSyslogServerEvent;
 import org.junit.Assert;
 
 import java.net.InetAddress;
+import java.util.HashMap;
 import java.util.Map;
 
 public class StructuredSyslogMessageTest extends TestCase
@@ -123,7 +123,7 @@ public class StructuredSyslogMessageTest extends TestCase
           fail();
 
       } catch (IllegalArgumentException iae) {
-          //
+          assertEquals("Invalid structured data in syslog message 'msgId1 [invalid SD] my message!!'", iae.getMessage());
       }
    }
 
@@ -136,7 +136,7 @@ public class StructuredSyslogMessageTest extends TestCase
           fail();
 
        } catch (IllegalArgumentException iae) {
-           //
+          assertEquals("Invalid structured data in syslog message 'msgId1 [data1 a=b] my message!!'", iae.getMessage());
        }
    }
 
@@ -149,7 +149,7 @@ public class StructuredSyslogMessageTest extends TestCase
           fail();
 
        } catch (IllegalArgumentException iae) {
-           //
+          assertEquals("Invalid structured data in syslog message 'msgId1 [data1 a=\"b] my message!!'", iae.getMessage());
        }
    }
 
@@ -162,7 +162,7 @@ public class StructuredSyslogMessageTest extends TestCase
           fail();
 
       } catch (IllegalArgumentException iae) {
-          //
+          assertEquals("Invalid structured data in syslog message 'msgId1 [data1 a=b\"] my message!!'", iae.getMessage());
       }
 
    }
@@ -214,13 +214,13 @@ public class StructuredSyslogMessageTest extends TestCase
    public void testCreateMessage3()
    {
       final StructuredSyslogMessage message =
-            new StructuredSyslogMessage("msgId", null, Maps.<String, Map<String, String>>newHashMap(), "my message");
+            new StructuredSyslogMessage("msgId", null, new HashMap<String, Map<String, String>>(), "my message");
       assertEquals("msgId [0@0] my message", message.createMessage());
    }
 
    public void testCreateMessage4()
    {
-      final Map<String, Map<String, String>> map = Maps.newHashMap();
+      final Map<String, Map<String, String>> map = new HashMap<String, Map<String, String>>();
       final StructuredSyslogMessage message =
             new StructuredSyslogMessage("msgId", null, map, "my message");
       assertEquals("msgId [0@0] my message", message.createMessage());