diff --git a/libcontainer/container_linux.go b/libcontainer/container_linux.go
index 95fd86bf8..ecb05a0d1 100644
--- a/libcontainer/container_linux.go
+++ b/libcontainer/container_linux.go
@@ -1146,8 +1146,9 @@ func (c *Container) bootstrapData(cloneFlags uintptr, nsMaps map[configs.Namespa
 		Value: c.config.RootlessEUID,
 	})
 
-	// write boottime and monotonic time ns offsets.
-	if c.config.TimeOffsets != nil {
+	// write boottime and monotonic time ns offsets only when we are not joining an existing time ns
+	_, joinExistingTime := nsMaps[configs.NEWTIME]
+	if !joinExistingTime && c.config.TimeOffsets != nil {
 		var offsetSpec bytes.Buffer
 		for clock, offset := range c.config.TimeOffsets {
 			fmt.Fprintf(&offsetSpec, "%s %d %d\n", clock, offset.Secs, offset.Nanosecs)
diff --git a/tests/integration/timens.bats b/tests/integration/timens.bats
index fb33e2b27..10f3fc057 100644
--- a/tests/integration/timens.bats
+++ b/tests/integration/timens.bats
@@ -54,6 +54,26 @@ function teardown() {
 	grep -E '^boottime\s+1337\s+3141519$' <<<"$output"
 }
 
+# https://github.com/opencontainers/runc/issues/4635
+@test "runc exec [simple timens]" {
+	requires timens
+
+	update_config '.process.args = ["sleep", "inf"]'
+	update_config '.linux.namespaces += [{"type": "time"}]
+		| .linux.timeOffsets = {
+			"monotonic": { "secs": 7881, "nanosecs": 2718281 },
+			"boottime": { "secs": 1337, "nanosecs": 3141519 }
+		}'
+
+	runc run -d --console-socket "$CONSOLE_SOCKET" test_busybox
+	[ "$status" -eq 0 ]
+
+	runc exec test_busybox cat /proc/self/timens_offsets
+	[ "$status" -eq 0 ]
+	grep -E '^monotonic\s+7881\s+2718281$' <<<"$output"
+	grep -E '^boottime\s+1337\s+3141519$' <<<"$output"
+}
+
 @test "runc run [simple timens + userns]" {
 	requires root
 	requires timens