diff --git a/api/server/server.go b/api/server/server.go
index bf1a157612..a2723d021b 100644
--- a/api/server/server.go
+++ b/api/server/server.go
@@ -272,14 +272,20 @@ func (s *Server) postContainersKill(version version.Version, w http.ResponseWrit
 	name := vars["name"]
 
 	// If we have a signal, look at it. Otherwise, do nothing
-	if sigStr := vars["signal"]; sigStr != "" {
+	if sigStr := r.Form.Get("signal"); sigStr != "" {
 		// Check if we passed the signal as a number:
 		// The largest legal signal is 31, so let's parse on 5 bits
-		sig, err := strconv.ParseUint(sigStr, 10, 5)
+		sigN, err := strconv.ParseUint(sigStr, 10, 5)
 		if err != nil {
 			// The signal is not a number, treat it as a string (either like
 			// "KILL" or like "SIGKILL")
-			sig = uint64(signal.SignalMap[strings.TrimPrefix(sigStr, "SIG")])
+			syscallSig, ok := signal.SignalMap[strings.TrimPrefix(sigStr, "SIG")]
+			if !ok {
+				return fmt.Errorf("Invalid signal: %s", sigStr)
+			}
+			sig = uint64(syscallSig)
+		} else {
+			sig = sigN
 		}
 
 		if sig == 0 {
diff --git a/integration-cli/docker_cli_kill_test.go b/integration-cli/docker_cli_kill_test.go
index 1371a0be08..8c0031a4a1 100644
--- a/integration-cli/docker_cli_kill_test.go
+++ b/integration-cli/docker_cli_kill_test.go
@@ -58,3 +58,62 @@ func (s *DockerSuite) TestKillDifferentUserContainer(c *check.C) {
 		c.Fatal("killed container is still running")
 	}
 }
+
+// regression test about correct signal parsing see #13665
+func (s *DockerSuite) TestKillWithSignal(c *check.C) {
+	runCmd := exec.Command(dockerBinary, "run", "-d", "busybox", "top")
+	out, _, err := runCommandWithOutput(runCmd)
+	c.Assert(err, check.IsNil)
+
+	cid := strings.TrimSpace(out)
+	c.Assert(waitRun(cid), check.IsNil)
+
+	killCmd := exec.Command(dockerBinary, "kill", "-s", "SIGWINCH", cid)
+	_, err = runCommand(killCmd)
+	c.Assert(err, check.IsNil)
+
+	running, err := inspectField(cid, "State.Running")
+	if running != "true" {
+		c.Fatal("Container should be in running state after SIGWINCH")
+	}
+}
+
+func (s *DockerSuite) TestKillWithInvalidSignal(c *check.C) {
+	runCmd := exec.Command(dockerBinary, "run", "-d", "busybox", "top")
+	out, _, err := runCommandWithOutput(runCmd)
+	c.Assert(err, check.IsNil)
+
+	cid := strings.TrimSpace(out)
+	c.Assert(waitRun(cid), check.IsNil)
+
+	killCmd := exec.Command(dockerBinary, "kill", "-s", "0", cid)
+	out, _, err = runCommandWithOutput(killCmd)
+	c.Assert(err, check.NotNil)
+	if !strings.ContainsAny(out, "Invalid signal: 0") {
+		c.Fatal("Kill with an invalid signal didn't error out correctly")
+	}
+
+	running, err := inspectField(cid, "State.Running")
+	if running != "true" {
+		c.Fatal("Container should be in running state after an invalid signal")
+	}
+
+	runCmd = exec.Command(dockerBinary, "run", "-d", "busybox", "top")
+	out, _, err = runCommandWithOutput(runCmd)
+	c.Assert(err, check.IsNil)
+
+	cid = strings.TrimSpace(out)
+	c.Assert(waitRun(cid), check.IsNil)
+
+	killCmd = exec.Command(dockerBinary, "kill", "-s", "SIG42", cid)
+	out, _, err = runCommandWithOutput(killCmd)
+	c.Assert(err, check.NotNil)
+	if !strings.ContainsAny(out, "Invalid signal: SIG42") {
+		c.Fatal("Kill with an invalid signal error out correctly")
+	}
+
+	running, err = inspectField(cid, "State.Running")
+	if running != "true" {
+		c.Fatal("Container should be in running state after an invalid signal")
+	}
+}