diff --git a/containerd/driver.go b/containerd/driver.go
index 4b28abe..17157d0 100644
--- a/containerd/driver.go
+++ b/containerd/driver.go
@@ -20,7 +20,6 @@ package containerd
 import (
 	"context"
 	"fmt"
-	"os"
 	"syscall"
 	"time"
 
@@ -583,13 +582,11 @@ func (d *Driver) SignalTask(taskID string, signal string) error {
 	// The given signal will be forwarded to the target taskID.
 	// Please checkout https://github.com/hashicorp/consul-template/blob/master/signals/signals_unix.go
 	// for a list of supported signals.
-	sig := os.Interrupt
-	if s, ok := signals.SignalLookup[signal]; ok {
-		sig = s
-	} else {
-		d.logger.Warn("unknown signal to send to task, using SIGINT instead", "signal", signal, "task_id", handle.taskConfig.ID)
-
+	sig, ok := signals.SignalLookup[signal]
+	if !ok {
+		return fmt.Errorf("Invalid signal: %s", signal)
 	}
+
 	return handle.signal(d.ctxContainerd, sig)
 }
 
diff --git a/tests/002-test-signal-handler.sh b/tests/002-test-signal-handler.sh
index e188571..d1e01e8 100755
--- a/tests/002-test-signal-handler.sh
+++ b/tests/002-test-signal-handler.sh
@@ -20,6 +20,23 @@ test_signal_handler_nomad_job() {
         exit 1
     fi
 
+    # Even though $(nomad job status) reports signal job status as "running"
+    # The actual container process might not be running yet.
+    # We need to wait for actual container to start running before trying to send invalid signal.
+    echo "INFO: Wait for signal container to get into RUNNING state, before trying to send invalid signal."
+    is_signal_container_active
+
+    echo "INFO: Test invalid signal."
+    alloc_id=$(nomad job status signal|awk 'END{print}'|cut -d ' ' -f 1)
+    local outfile=$(mktemp /tmp/signal.XXXXXX)
+    nomad alloc signal -s INVALID $alloc_id >> $outfile 2>&1
+    if ! grep -q "Invalid signal" $outfile; then
+        echo "ERROR: Invalid signal didn't error out."
+        cleanup "$outfile"
+        exit 1
+    fi
+    cleanup "$outfile"
+
     echo "INFO: Stopping nomad signal handler job."
     nomad job stop signal
     signal_status=$(nomad job status -short signal|grep Status|awk '{split($0,a,"="); print a[2]}'|tr -d ' ')
@@ -33,4 +50,29 @@ test_signal_handler_nomad_job() {
     popd
 }
 
+cleanup() {
+  local tmpfile=$1
+  rm $tmpfile > /dev/null 2>&1
+}
+
+is_signal_container_active() {
+        i="0"
+        while test $i -lt 5
+        do
+                sudo CONTAINERD_NAMESPACE=nomad ctr task ls|grep -q RUNNING
+                if [ $? -eq 0 ]; then
+                        echo "INFO: signal container is up and running"
+                        break
+                fi
+                echo "INFO: signal container is down, sleep for 4 seconds."
+                sleep 4s
+                i=$[$i+1]
+        done
+
+        if [ $i -ge 5 ]; then
+                echo "ERROR: signal container didn't come up. exit 1."
+                exit 1
+        fi
+}
+
 test_signal_handler_nomad_job
diff --git a/tests/003-test-capabilities.sh b/tests/003-test-capabilities.sh
index 3b16310..3b9a648 100755
--- a/tests/003-test-capabilities.sh
+++ b/tests/003-test-capabilities.sh
@@ -81,6 +81,7 @@ is_capabilities_container_active() {
                 sudo CONTAINERD_NAMESPACE=nomad ctr task ls|grep -q RUNNING
                 if [ $? -eq 0 ]; then
                         echo "INFO: capabilities container is up and running"
+                        sleep 5s
                         break
                 fi
                 echo "INFO: capabilities container is down, sleep for 4 seconds."