diff --git a/changelog.md b/changelog.md
index bc595dcce..513a1a570 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,5 +1,6 @@
 ## Fixes/improvements
 
+* [#3621] Fix `os.time()` being off by one hour
 * [#3682] Add error handling to the `flash` OpenOS program
 * [#3764] Fix left and right names being swapped in the Rack GUI
 * [#3779] Fix `os.sleep(0)` causing `too long without yielding` (Ocawesome101)
diff --git a/src/main/scala/li/cil/oc/server/machine/luac/OSAPI.scala b/src/main/scala/li/cil/oc/server/machine/luac/OSAPI.scala
index 56773404f..9d539f356 100644
--- a/src/main/scala/li/cil/oc/server/machine/luac/OSAPI.scala
+++ b/src/main/scala/li/cil/oc/server/machine/luac/OSAPI.scala
@@ -67,10 +67,11 @@ class OSAPI(owner: NativeLuaArchitecture) extends NativeLuaAPI(owner) {
       if (lua.isNoneOrNil(1)) {
         // Game time is in ticks, so that each day has 24000 ticks, meaning
         // one hour is game time divided by one thousand. Also, Minecraft
-        // starts days at 6 o'clock, versus the 1 o'clock of timestamps so we
-        // add those five hours. Thus:
-        // timestamp = (time + 5000) * 60[kh] * 60[km] / 1000[s]
-        lua.pushNumber(((machine.worldTime + 5000) * 60 * 60) / 1000.0)
+        // starts days at 6 o'clock; os.time() reflects UTC while os.date()
+        // reflects the local time zone, but Minecraft has no concept of
+        // time zones, so this detail can be ignored. Thus:
+        // timestamp = (time + 6000) * 60[kh] * 60[km] / 1000[s]
+        lua.pushNumber(((machine.worldTime + 6000) * 60 * 60) / 1000.0)
       }
       else {
         def getField(key: String, d: Int) = {
diff --git a/src/main/scala/li/cil/oc/server/machine/luaj/OSAPI.scala b/src/main/scala/li/cil/oc/server/machine/luaj/OSAPI.scala
index 06e721194..41b3e0e39 100644
--- a/src/main/scala/li/cil/oc/server/machine/luaj/OSAPI.scala
+++ b/src/main/scala/li/cil/oc/server/machine/luaj/OSAPI.scala
@@ -51,10 +51,11 @@ class OSAPI(owner: LuaJLuaArchitecture) extends LuaJAPI(owner) {
       if (args.isnoneornil(1)) {
         // Game time is in ticks, so that each day has 24000 ticks, meaning
         // one hour is game time divided by one thousand. Also, Minecraft
-        // starts days at 6 o'clock, versus the 1 o'clock of timestamps so we
-        // add those five hours. Thus:
-        // timestamp = (time + 5000) * 60[kh] * 60[km] / 1000[s]
-        LuaValue.valueOf((machine.worldTime + 5000) * 60 * 60 / 1000)
+        // starts days at 6 o'clock; os.time() reflects UTC while os.date()
+        // reflects the local time zone, but Minecraft has no concept of
+        // time zones, so this detail can be ignored. Thus:
+        // timestamp = (time + 6000) * 60[kh] * 60[km] / 1000[s]
+        LuaValue.valueOf((machine.worldTime + 6000) * 60 * 60 / 1000)
       }
       else {
         val table = args.checktable(1)