diff --git a/libcontainer/factory_linux.go b/libcontainer/factory_linux.go
index e6c71ac34..1df87e2e5 100644
--- a/libcontainer/factory_linux.go
+++ b/libcontainer/factory_linux.go
@@ -179,6 +179,12 @@ func (l *LinuxFactory) Create(id string, config *configs.Config) (Container, err
 			return nil, fmt.Errorf("unable to get cgroup PIDs: %w", err)
 		}
 		if len(pids) != 0 {
+			if config.Cgroups.Systemd {
+				// systemd cgroup driver can't add a pid to an
+				// existing systemd unit and will return an
+				// error anyway, so let's error out early.
+				return nil, fmt.Errorf("container's cgroup is not empty: %d process(es) found", len(pids))
+			}
 			// TODO: return an error.
 			logrus.Warnf("container's cgroup is not empty: %d process(es) found", len(pids))
 			logrus.Warn("DEPRECATED: running container in a non-empty cgroup won't be supported in runc 1.2; https://github.com/opencontainers/runc/issues/3132")
diff --git a/tests/integration/cgroups.bats b/tests/integration/cgroups.bats
index ff7cf6d0b..7fd2e30af 100644
--- a/tests/integration/cgroups.bats
+++ b/tests/integration/cgroups.bats
@@ -348,7 +348,7 @@ function setup() {
 	[ "$output" = "ok" ]
 }
 
-@test "runc run/create should warn about a non-empty cgroup" {
+@test "runc run/create should error/warn about a non-empty cgroup" {
 	if [[ "$ROOTLESS" -ne 0 ]]; then
 		requires rootless_cgroup
 	fi
@@ -358,14 +358,21 @@ function setup() {
 	runc run -d --console-socket "$CONSOLE_SOCKET" ct1
 	[ "$status" -eq 0 ]
 
+	# When systemd driver is used, runc can't add PID to an existing unit,
+	# so runc returns an error. For backward compatibility, we still allow
+	# such configuration in 1.1, but only when systemd driver is NOT used.
+	# See https://github.com/opencontainers/runc/issues/3780.
+	local exp=0
+	[[ -n "${RUNC_USE_SYSTEMD}" ]] && exp=1
+
 	# Run a second container sharing the cgroup with the first one.
 	runc --debug run -d --console-socket "$CONSOLE_SOCKET" ct2
-	[ "$status" -eq 0 ]
+	[ "$status" -eq "$exp" ]
 	[[ "$output" == *"container's cgroup is not empty"* ]]
 
 	# Same but using runc create.
 	runc create --console-socket "$CONSOLE_SOCKET" ct3
-	[ "$status" -eq 0 ]
+	[ "$status" -eq "$exp" ]
 	[[ "$output" == *"container's cgroup is not empty"* ]]
 }