diff --git a/htrace-zipkin/pom.xml b/htrace-zipkin/pom.xml
index d4225f0..3727513 100644
--- a/htrace-zipkin/pom.xml
+++ b/htrace-zipkin/pom.xml
@@ -27,6 +27,7 @@
 
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <slf4j.version>1.5.8</slf4j.version>
   </properties>
 
   <build>
@@ -140,11 +141,19 @@
       <artifactId>libthrift</artifactId>
       <version>0.9.0</version>
     </dependency>
+
     <dependency>
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-nop</artifactId>
-      <version>1.5.8</version>
+      <version>${slf4j.version}</version>
     </dependency>
+
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-api</artifactId>
+      <version>${slf4j.version}</version>
+    </dependency>
+
     <dependency>
       <groupId>commons-codec</groupId>
       <artifactId>commons-codec</artifactId>