diff --git a/Makefile b/Makefile
index 0251ae10453..ef22f69ff76 100644
--- a/Makefile
+++ b/Makefile
@@ -66,4 +66,4 @@ clean_tidb:
 
 clean:
 	cargo clean
-	@rm -rf $(DEPS_PATH) $(BIN_PATH)
\ No newline at end of file
+	@rm -rf $(DEPS_PATH) $(BIN_PATH)
diff --git a/tests/raftstore/cluster.rs b/tests/raftstore/cluster.rs
index d3a76d45142..c942a079769 100644
--- a/tests/raftstore/cluster.rs
+++ b/tests/raftstore/cluster.rs
@@ -173,7 +173,7 @@ impl<T: Simulator> Cluster<T> {
         let region_id = request.get_header().get_region_id();
         loop {
             let leader = match self.leader_of_region(region_id) {
-                None => return Err(box_err!("can't get leader of region")),
+                None => return Err(box_err!("can't get leader of region {}", region_id)),
                 Some(l) => l,
             };
             request.mut_header().set_peer(leader);
diff --git a/tests/raftstore/util.rs b/tests/raftstore/util.rs
index 298ca780e71..9089b33f50c 100644
--- a/tests/raftstore/util.rs
+++ b/tests/raftstore/util.rs
@@ -68,7 +68,7 @@ pub fn new_store_cfg() -> Config {
     Config {
         raft_base_tick_interval: 10,
         raft_heartbeat_ticks: 2,
-        raft_election_timeout_ticks: 20,
+        raft_election_timeout_ticks: 25,
         raft_log_gc_tick_interval: 100,
         raft_log_gc_threshold: 1,
         pd_heartbeat_tick_interval: 20,
diff --git a/travis-build/Makefile b/travis-build/Makefile
index c34c30ad3f5..9a657e26918 100644
--- a/travis-build/Makefile
+++ b/travis-build/Makefile
@@ -71,6 +71,7 @@ cover_linux:
 	export LIBRARY_PATH="${LIBRARY_PATH}:${ROCKSDB_DIR}" && \
 	export LOG_LEVEL=DEBUG && \
 	export RUST_BACKTRACE=1 && \
+	export RUST_TEST_THREADS=1 && \
 	grep " Running " tests.out | sed -e 's/Running//g' | xargs -n 1 -i ${KCOV_DIR}/kcov --verify --coveralls-id=${TRAVIS_JOB_ID} --include-pattern tikv/src --exclude-pattern tikv/src/bin --strip-path `pwd`/ target/kcov {} --nocapture
 
 cover_osx:
diff --git a/travis-build/test.sh b/travis-build/test.sh
index b5e290554a3..d4ab8869433 100755
--- a/travis-build/test.sh
+++ b/travis-build/test.sh
@@ -26,6 +26,7 @@ fi
 
 export ENABLE_FEATURES=default
 export LOG_FILE=tests.log
+export RUST_TEST_THREADS=1
 make test 2>&1 | tee tests.out
 status=$?
 for case in `cat tests.out | python -c "import sys
@@ -41,10 +42,12 @@ print '\n'.join(cases)
 "`; do
     echo find fail cases: $case
     grep $case $LOG_FILE | cut -d ' ' -f 2-
+    # there is a thread panic, which should not happen.
+    status=1
     echo
 done
 
-rm tests.out || true
+# don't remove the tests.out, coverage counts on it.
 rm $LOG_FILE || true
 
 exit $status