--- title: "Fixed the Mac Civ V crash when an AI recaptures its capital" url: "https://reamcp.dev/en/cases/fixed-the-mac-civ-v-crash-when-an-ai-recaptures-its-capital-c10faf" source: "https://github.com/jtutlis/civ5-mac-capital-crash-fix" source_type: "github" repo: "https://github.com/jtutlis/civ5-mac-capital-crash-fix" author: "jtutlis1" author_handle: "jtutlis1" stars: 0 category: "Patches & fixes" categories: ["patches-fixes"] tags: ["civilization-v", "crash-analysis", "game-binary-patching", "macos", "reverse-engineering"] added: "2026-10-13T03:39:22.266Z" updated: "2026-10-11T19:31:19Z" locale: "en" content_locale: "en" --- # Fixed the Mac Civ V crash when an AI recaptures its capital A Civ V player used Claude + REA to diagnose a recurring macOS crash triggered when an AI recaptures its capital, and published a binary patch to fix it. ## Description The author describes a long-standing crash in the Mac version of Civilization V that occurred roughly once every ten games when a civilization recaptured its capital. After failing to find an existing fix, they used Claude together with REA to track down the root cause and produced a patch, published at https://github.com/jtutlis/civ5-mac-capital-crash-fix. The fix is applied by patching the game binary rather than as a mod, since mods would disable achievements. ## Original README # Civ V Mac: capital recapture crash fix A binary patch for **Sid Meier's Civilization V on macOS** (Steam, Brave New World) that fixes a crash when a civilization recaptures its original capital. > Not affiliated with Firaxis, Aspyr or 2K. This repository contains no game files; the patch > modifies your own installed copy and keeps a backup. ## The bug In Brave New World games the game crashes to desktop right after a civilization takes back its original capital. It happens whenever no single team holds the most original capitals at that moment, for example when every civ holds just its own capital. If your crash report (`~/Library/Logs/DiagnosticReports/Civilization V-*.ips`) looks like this, this is your bug: ``` Exception Type: EXC_BAD_ACCESS (SIGSEGV) Thread N Crashed:: WinMain (WinID 2) 0 ??? 0x... ??? 1 libCvGameCoreDLL_Expansion2_DLL.dylib 0x... 0x... + 3013620 2 libCvGameCoreDLL_Expansion2_DLL.dylib 0x... 0x... + 2995429 ``` ## Requirements - macOS, Steam version of Civilization V with Brave New World. Tested on Apple silicon (the game runs under Rosetta) on macOS 26.4. - The supported game core build: `libCvGameCoreDLL_Expansion2_DLL.dylib` with sha256 `0da6a5ffc283c3f147b20a7ec426e4ed85a6838ab891faf61b50af4e25c4a09c`. The script checks this and refuses to patch any other version. Only built-in macOS tools are used (`bash`, `dd`, `od`, `shasum`, `codesign`). ## Install 1. Quit Civilization V. 2. Download this repository (green **Code** button → **Download ZIP**, or `git clone`) and open Terminal in its folder. 3. Run: ```sh ./patch.sh apply ``` Check the state at any time with `./patch.sh status`. If your Steam library is not in the default location, point the script at the game core: ```sh CIV5_GAMECORE="/path/to/Civilization V.app/Contents/MacOS/libCvGameCoreDLL_Expansion2_DLL.dylib" ./patch.sh apply ``` **After a game update or Steam's "Verify integrity of game files"**, Steam restores the original file. Run `./patch.sh apply` again. ## Uninstall ```sh ./patch.sh revert ``` or use Steam's **Properties → Installed Files → Verify integrity of game files**. ## FAQ **Can this get me banned?** Civilization V does not use Valve Anti-Cheat (VAC), and Firaxis publishes the game core's source so players can replace it. Mods such as the Community Patch (Vox Populi) have replaced this library for years. **Does it disable achievements?** No. It doesn't use the in-game mod system, which is what turns achievements off. **Multiplayer?** Everyone in a multiplayer game should run the same game core. Mixing patched and unpatched players is untested and may cause desyncs. **Windows?** This patch only targets the macOS build. ## How it works The crash is in `CvPlayer::SetHasLostCapital(bool bValue, PlayerTypes eConqueror)` (address `0x2de2d0` in the stripped library). When a capital changes hands, the function counts original capitals per team to find which team is "winning", which the notification text mentions. If no single team leads, the winning team is `NO_TEAM` (`-1`). When building the "you recovered your capital" notification for the civ that just regained its capital, the code calls `GET_TEAM(eMyTeam).isHasMet(eWinningTeam)` without checking for `NO_TEAM`. `isHasMet` is `return m_abHasMet[eIndex];`, compiled as: ```asm movl %esi, %eax ; zero-extends -1 to 0x00000000ffffffff movb 0x738(%rdi,%rax), %al ; reads ~4 GB past the CvTeam object -> SIGSEGV ``` In 32-bit builds this would read one byte before the array and carry on. The 64-bit Mac build reads unmapped memory and crashes. The "lost capital" path and the notifications sent to other players already check for `NO_TEAM`; this one path doesn't. The patch adds that check, jumping to the code the function already has for the no-winner case (the plain "you recovered your capital" text). It needs 10 bytes, taken from a redundant bounds check on the player's own ID, which is always valid: ```asm ; before (0x2dfbba) ; after (0x2dfbba) movq -0x38(%rbp), %rax cmpl $-0x1, -0x50(%rbp) ; eWinningTeam == NO_TEAM? movslq (%rax), %rax je 0x2dfca8 ; no-winner notification movl $0xffffffff, %ecx movq -0x38(%rbp), %rax cmpq $0x3f, %rax movslq (%rax), %rax ja 0x2dfbd6 movq -0x60(%rbp), %rcx movq -0x60(%rbp), %rcx movq (%rcx), %rcx movq (%rcx), %rcx movl (%rcx,%rax,4), %ecx movl (%rcx,%rax,4), %ecx nop ``` 28 bytes change in total. Editing the code invalidates the library's ad hoc code signature, so the script re-signs it ad hoc (`codesign --sign -`), which is how it was originally signed. ## Reproducing the crash `test/` contains a small Lua mod that stages the crash on turn 2: one AI captures another AI's original capital, and the owner immediately recaptures it. ```sh test/civ5test.sh setup # install the test mod, enable Lua logging ./patch.sh revert # optional: start with the original game core ``` 1. Launch Civ V → **Mods** → enable **Capital Recapture Test** → **Single Player** → **Set Up Game** with at least two AI civs. 2. Press **End Turn** until turn 2. - Original game core: the game crashes. - Patched: notifications show an unmet player losing and then regaining its capital, and the game keeps running. 3. To rerun quickly, load the turn 1 autosave from the Mods menu and press **End Turn**. ```sh test/civ5test.sh result # test log lines (Lua.log is written on exit) and new crash reports ./patch.sh apply # switch to the patched game core test/civ5test.sh teardown # remove the mod and restore the logging setting ``` Achievements are disabled while the test mod is active; run `teardown` when you're done. ## Credits Found with [REA](https://github.com/morluto/rea) and Hopper Disassembler, using a crash report to locate the faulting instruction. ## License MIT. See [LICENSE](LICENSE).