diff --git a/Dist/wrapper-scripts.nix b/Dist/wrapper-scripts.nix
index aa485bca03..ce3bff512d 100644
--- a/Dist/wrapper-scripts.nix
+++ b/Dist/wrapper-scripts.nix
@@ -58,7 +58,7 @@ in rec {
 		fi
 
 		export LD_LIBRARY_PATH=$BIZHAWK_HOME/dll:$BIZHAWK_GLHACKDIR:${lib.makeLibraryPath [ openal ]}
-		${commentUnless debugPInvokes}MONO_LOG_LEVEL=debug MONO_LOG_MASK=dll
+		${commentUnless debugPInvokes}export MONO_LOG_LEVEL=debug MONO_LOG_MASK=dll
 		if [ "$1" = "--mono-no-redirect" ]; then
 			shift
 			printf "(received --mono-no-redirect, stdout was not captured)\n" >EmuHawkMono_laststdout.txt
diff --git a/default.nix b/default.nix
index f80726fb71..d2ef120e7e 100644
--- a/default.nix
+++ b/default.nix
@@ -1,4 +1,5 @@
 # THIS IS A WORK IN PROGRESS!
+# To save you having to build Mono locally, install the Cachix client (`nix-env -iA nixpkgs.cachix`) and run `cachix use mono-for-bizhawk` (both commands only need to run once ever). See https://docs.cachix.org for more info.
 
 { pkgs ? import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/21.11.tar.gz") {}
 # infrastructure
@@ -9,26 +10,33 @@
 , makeWrapper ? pkgs.makeWrapper
 # source
 , useCWDAsSource ? false
-, hawkVersion ? if useCWDAsSource then "2.7.1-local" else "2.7" # used to distinguish parallel installs' config and other data
-, hawkSource ? if useCWDAsSource
-	then builtins.path {
-		path = ./.;
-		name = "BizHawk-${hawkVersion}";
-		filter = let
-			denyList = [ ".idea" "ExternalCoreProjects" "ExternalProjects" "ExternalToolProjects" "libHawk" "libmupen64plus" "LibretroBridge" "LuaInterface" "lynx" "psx" "quicknes" "submodules" "waterbox" "wonderswan" ];
-		in path: type: type == "regular" || (type == "directory" && !builtins.elem (baseNameOf path) denyList);
+, hawkSourceInfo ? if useCWDAsSource
+	then rec {
+		version = "2.7.1-local"; # distinguishes parallel installs' config and other data
+		shorthash = "000000000"; # this and the branch name are written into movies and savestates, written to config to detect in-place upgrades (N/A to Nix), and of course also shown in the About dialog
+		branch = "master"; # must be regex-escaped (interpolated as `sed "s/.../${branch}/"`)
+		drv = builtins.path {
+			path = ./.;
+			name = "BizHawk-${version}";
+			filter = let # this is just for speed, not any r13y concern
+				denyList = [ ".idea" "ExternalCoreProjects" "ExternalProjects" "ExternalToolProjects" "libHawk" "libmupen64plus" "LibretroBridge" "LuaInterface" "lynx" "psx" "quicknes" "submodules" "waterbox" "wonderswan" ];
+			in path: type: type == "regular" || (type == "directory" && !builtins.elem (baseNameOf path) denyList);
+		};
 	}
-	else fetchFromGitHub {
-		owner = "TASEmulators";
-		repo = "BizHawk";
-		rev = "dbaf2595625f79093eeec37d2d4a7a9a4d37f370";
-		hash = "sha256-AQhnBy8lSiuFqA6I7lk6M1u3osAJEoEMELGDgGC/aII="; # changes randomly? maybe when submodules are changed? --yoshi
-		leaveDotGit = true;
+	else {
+		version = "2.7";
+		shorthash = "dbaf25956";
+		branch = "master";
+		drv = fetchFromGitHub {
+			owner = "TASEmulators";
+			repo = "BizHawk";
+			rev = "dbaf2595625f79093eeec37d2d4a7a9a4d37f370";
+			hash = "sha256-KXe69svPIIFaXgT9t+02pwdQ6WWqdqgUdtaE2S4/YxA=";
+		};
 	}
 # makedeps
 , dotnet-sdk_5 ? pkgs.dotnetCorePackages.sdk_5_0
 , dotnet-sdk_6 ? pkgs.dotnetCorePackages.sdk_6_0
-, git ? pkgs.git
 , p7zip ? pkgs.p7zip
 # rundeps for NixOS hosts
 #, gtk2-x11 ? pkgs.gtk2-x11
@@ -55,14 +63,21 @@ let
 			else pkgs.callPackage Dist/mono-6.12.0.151.nix {}; # not actually reproducible :( https://github.com/NixOS/nixpkgs/issues/143110#issuecomment-984251253
 	bizhawk = buildDotnetModule rec {
 		pname = "BizHawk";
-		version = hawkVersion;
-		src = hawkSource;
+		version = hawkSourceInfo.version;
+		src = hawkSourceInfo.drv;
 		dotnet-sdk = if useCWDAsSource then dotnet-sdk_6 else dotnet-sdk_5;
-		nativeBuildInputs = [ git p7zip ];
+		nativeBuildInputs = [ p7zip ];
 		buildInputs = [ mesa monoFinal openal uname ];# ++ lib.optionals (forNixOS) [ gtk2-x11 ];
 		projectFile = "BizHawk.sln";
 		nugetDeps = if useCWDAsSource then Dist/deps.nix else Dist/deps-old.nix;
 		extraDotnetBuildFlags = "-maxcpucount:$NIX_BUILD_CORES -p:BuildInParallel=true --no-restore";
+		postPatch = ''
+			# confused? '$(...)' is literal here
+			# these scripts invoke Git in subshells and we want to run them now, at compile time, without Git
+			sed -i 's/$(git rev-parse --verify HEAD)/${hawkSourceInfo.shorthash}/' Dist/.InvokeCLIOnMainSln.sh
+			sed -i -e 's/$(git rev-parse --abbrev-ref HEAD)/${hawkSourceInfo.branch}/' -e 's/$(git log -1 --format="%h")/${hawkSourceInfo.shorthash}/' Build/standin.sh
+			sed -i 's/$(git rev-list HEAD --count)//' Build/standin.sh # const field is unused
+		'';
 		buildPhase = ''
 			${commentUnless useCWDAsSource}cd src/BizHawk.Version
 			${commentUnless useCWDAsSource}dotnet build ${extraDotnetBuildFlags}
@@ -89,14 +104,15 @@ let
 	};
 	wrapperScripts = import Dist/wrapper-scripts.nix {
 		inherit (pkgs) lib writeShellScriptBin writeText;
-		inherit commentUnless versionAtLeast mesa openal debugPInvokes hawkVersion initConfig;
+		inherit commentUnless versionAtLeast mesa openal debugPInvokes initConfig;
+		hawkVersion = hawkSourceInfo.version;
 		mono = monoFinal;
 	};
 in {
 	bizhawkAssemblies = bizhawk;
 	emuhawk = stdenv.mkDerivation rec {
 		pname = "emuhawk-monort";
-		version = hawkVersion;
+		version = hawkSourceInfo.version;
 		nativeBuildInputs = [ makeWrapper ];
 		buildInputs = [ bizhawk ];
 		# there must be a helper for this somewhere...