diff --git a/Makefile b/Makefile
index 35cf67e..b663cc8 100644
--- a/Makefile
+++ b/Makefile
@@ -171,6 +171,8 @@ test: $(BIN) $(TEST_BINS) test-cmdline
 ifeq ($(UID),0)
 	$(call run_test, setpriv --reuid 1000 --regid 1000 --groups 1234 -- ./nsjail -q -Mo --user 65534 --group 65534 --disable_clone_newnet --disable_clone_newcgroup --disable_clone_newns --disable_clone_newpid --disable_clone_newipc --disable_clone_newuts --disable_proc -- /bin/true, 255)
 	$(call run_test, setpriv --reuid 1000 --regid 1000 --clear-groups -- ./nsjail -q -Mo --user 65534 --group 65534 --disable_clone_newnet --disable_clone_newcgroup --disable_clone_newns --disable_clone_newpid --disable_clone_newipc --disable_clone_newuts --disable_proc -- /bin/true, 0)
+	$(call run_test, setsid --fork --wait ./nsjail -q -Me --disable_clone_newuser --disable_clone_newnet --disable_clone_newcgroup --disable_clone_newns --disable_clone_newpid --disable_clone_newipc --disable_clone_newuts --disable_proc --chroot / -- /bin/true, 0)
+	$(call run_test, strace -f -qq -e inject=setsid:error=EPERM ./nsjail -q -Me --disable_clone_newuser --disable_clone_newnet --disable_clone_newcgroup --disable_clone_newns --disable_clone_newpid --disable_clone_newipc --disable_clone_newuts --disable_proc --chroot / -- /bin/true, 255)
 endif
 	$(call run_test, ./nsjail -q -Mo --chroot / --user 99999 --group 99999 -- /bin/true < /tmp, 255)
 	$(call run_test, ./nsjail -q -Mo --chroot / --user 99999 --group 99999 --pass_fd 0 -- /bin/true < /tmp, 0)
diff --git a/contain.cc b/contain.cc
index 8ad6f57..06c7534 100644
--- a/contain.cc
+++ b/contain.cc
@@ -147,7 +147,16 @@ static bool containPrepareEnv(nsj_t* nsj, int parent_fd, pid_t expected_parent)
 		PLOG_W("setpriority(%d)", nsj->njc.nice_level());
 	}
 	if (!nsj->njc.skip_setsid()) {
-		setsid();
+		if (setsid() == -1) {
+			const int saved_errno = errno;
+			if (saved_errno == EPERM && getsid(0) == getpid()) {
+				LOG_D("Process is already a session leader (SID == PID)");
+			} else {
+				errno = saved_errno;
+				PLOG_E("setsid()");
+				return false;
+			}
+		}
 	}
 	return true;
 }