diff --git a/src/main/java/com/jcabi/ssh/Shell.java b/src/main/java/com/jcabi/ssh/Shell.java
index f948d38..94b6362 100644
--- a/src/main/java/com/jcabi/ssh/Shell.java
+++ b/src/main/java/com/jcabi/ssh/Shell.java
@@ -103,7 +103,7 @@ public int exec(final String command, final InputStream stdin,
             final int exit = this.origin.exec(command, stdin, stdout, stderr);
             if (exit != 0) {
                 throw new IllegalArgumentException(
-                    String.format("exit code #%d: %s", exit, command)
+                    String.format("non-zero exit code #%d: %s", exit, command)
                 );
             }
             return exit;
diff --git a/src/test/java/com/jcabi/ssh/SSHDTest.java b/src/test/java/com/jcabi/ssh/SSHDTest.java
index d64bf1e..85ce3ca 100644
--- a/src/test/java/com/jcabi/ssh/SSHDTest.java
+++ b/src/test/java/com/jcabi/ssh/SSHDTest.java
@@ -72,7 +72,9 @@ public void executeCommandOnServer() throws Exception {
         final SSHD sshd = new SSHD(this.temp.newFolder());
         try {
             MatcherAssert.assertThat(
-                new Shell.Plain(sshd.connect()).exec("echo one"),
+                new Shell.Plain(
+                    new Shell.Safe(sshd.connect())
+                ).exec("echo one"),
                 Matchers.startsWith("one")
             );
         } finally {
@@ -90,9 +92,11 @@ public void executeCommandOnServerWithManualConfig() throws Exception {
         try {
             MatcherAssert.assertThat(
                 new Shell.Plain(
-                    new SSH(
-                        sshd.host(), sshd.port(), sshd.login(),
-                        this.getClass().getResource("id_rsa")
+                    new Shell.Safe(
+                        new SSH(
+                            sshd.host(), sshd.port(), sshd.login(),
+                            this.getClass().getResource("id_rsa")
+                        )
                     )
                 ).exec("echo 'how are you'"),
                 Matchers.startsWith("how are")