diff --git a/src/lib-smtp/test-smtp-server-errors.c b/src/lib-smtp/test-smtp-server-errors.c
index d1bddbcd9f..65fd399b77 100644
--- a/src/lib-smtp/test-smtp-server-errors.c
+++ b/src/lib-smtp/test-smtp-server-errors.c
@@ -48,6 +48,7 @@ static struct ip_addr bind_ip;
 static in_port_t bind_port = 0;
 static struct ioloop *ioloop;
 static bool debug = FALSE;
+static volatile bool killing_children = FALSE;
 
 /* server */
 static struct smtp_server *smtp_server = NULL;
@@ -1478,20 +1479,32 @@ static int test_open_server_fd(void)
 	return fd;
 }
 
+static void test_clients_kill_one(unsigned int index, pid_t pid)
+{
+	(void)kill(pid, SIGKILL);
+	if (waitpid(pid, NULL, 0) < 0 &&
+	    errno == ECHILD) {
+		test_out_quiet(
+			t_strdup_printf("client [%u] (pid=%u) still running",
+					index, (unsigned int)pid), FALSE);
+	}
+}
+
 static void test_clients_kill_all(void)
 {
 	unsigned int i;
 
+	killing_children = TRUE;
 	if (client_pids_count > 0) {
 		for (i = 0; i < client_pids_count; i++) {
 			if (client_pids[i] != (pid_t)-1) {
-				(void)kill(client_pids[i], SIGKILL);
-				(void)waitpid(client_pids[i], NULL, 0);
+				test_clients_kill_one(i+1, client_pids[i]);
 				client_pids[i] = -1;
 			}
 		}
 	}
 	client_pids_count = 0;
+	killing_children = FALSE;
 }
 
 static void test_run_client_server(
@@ -1532,10 +1545,14 @@ static void test_run_client_server(
 				client_test(i);
 				io_loop_destroy(&ioloop);
 				i_free(client_pids);
+
+				if (debug)
+					i_debug("Waiting to be killed");
 				/* wait for it to be killed; this way, valgrind
 				   will not object to this process going away
 				   inelegantly. */
 				sleep(60);
+
 				exit(1);
 			}
 		}
@@ -1577,6 +1594,22 @@ test_signal_handler(int signo)
 	raise(signo);
 }
 
+static void
+test_child_handler(int signo ATTR_UNUSED)
+{
+	int saved_errno = errno;
+
+	if (killing_children) {
+		/* waitpid() is used in test_clients_kill_all() to check
+		   whether child was still running. Therefore, we must not
+		   wait for it here when that is happening. */
+		return;
+	}
+
+	while (waitpid((pid_t)(-1), 0, WNOHANG) > 0) {}
+	errno = saved_errno;
+}
+
 static void test_atexit(void)
 {
 	test_clients_kill_all();
@@ -1587,12 +1620,12 @@ int main(int argc, char *argv[])
 	int c;
 
 	atexit(test_atexit);
-	(void)signal(SIGCHLD, SIG_IGN);
 	(void)signal(SIGTERM, test_signal_handler);
 	(void)signal(SIGQUIT, test_signal_handler);
 	(void)signal(SIGINT, test_signal_handler);
 	(void)signal(SIGSEGV, test_signal_handler);
 	(void)signal(SIGABRT, test_signal_handler);
+	(void)signal(SIGCHLD, test_child_handler);
 
 	while ((c = getopt(argc, argv, "D")) > 0) {
 		switch (c) {