diff --git a/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/web/client/feign/TracingFeignClient.java b/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/web/client/feign/TracingFeignClient.java
index f21553525..c99573f26 100644
--- a/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/web/client/feign/TracingFeignClient.java
+++ b/spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/web/client/feign/TracingFeignClient.java
@@ -18,10 +18,9 @@ package org.springframework.cloud.sleuth.instrument.web.client.feign;
 
 import java.io.IOException;
 import java.nio.charset.Charset;
-import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.HashMap;
-import java.util.List;
 import java.util.Map;
 
 import brave.Span;
@@ -51,9 +50,14 @@ final class TracingFeignClient implements Client {
 		@Override public void put(Map<String, Collection<String>> carrier, String key,
 				String value) {
 			if (!carrier.containsKey(key)) {
-				List<String> list = new ArrayList<>();
-				list.add(value);
-				carrier.put(key, list);
+				carrier.put(key, Collections.singletonList(value));
+				if (log.isTraceEnabled()) {
+					log.trace("Added key [" + key + "] and header value [" + value + "]");
+				}
+			} else {
+				if (log.isTraceEnabled()) {
+					log.trace("Key [" + key + "] already there in the headers");
+				}
 			}
 		}
 
diff --git a/spring-cloud-sleuth-core/src/test/resources/application.yml b/spring-cloud-sleuth-core/src/test/resources/application.yml
index c2916927c..dcd3c7284 100644
--- a/spring-cloud-sleuth-core/src/test/resources/application.yml
+++ b/spring-cloud-sleuth-core/src/test/resources/application.yml
@@ -17,6 +17,7 @@ spring.sleuth.scheduled.skipPattern: "^org.*TestBeanWithScheduledMethodToBeIgnor
 spring.sleuth.rxjava.schedulers.ignoredthreads: HystixMetricPoller,^MyCustomThread.*$,^RxComputation.*$
 
 logging.level.org.springframework.cloud: DEBUG
+logging.level.org.springframework.cloud.sleuth.instrument.web.client.feign: TRACE
 
 #disable hibernate by default
 spring.autoconfigure.exclude: org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration, org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration, org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration
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