diff --git a/tools/macOS/builder b/tools/macOS/builder
index a817cf2c..c666b880 100755
--- a/tools/macOS/builder
+++ b/tools/macOS/builder
@@ -116,6 +116,12 @@ best_llvm_path=$(
 # Fallback to XCode version.
 [ -z "$best_llvm_path" ] && best_llvm_path=/usr
 
+case "$best_llvm_path" in
+    /nix/store/*) # Nix
+        rt_lib=$(find /nix/store -maxdepth 1 -type d -name '*-compiler-rt-libc-*[0-9]' | while read -r d; do echo $d $(echo $d | sed -E 's/.*-([0-9.]+)$/\1/'); done | sort -V -k 2 | tail -n 1 | awk '{ print $1 }')/lib/libclang_rt.osx.a
+        ;;
+esac
+
 clang_path=${best_llvm_path%%:*}
 xcode_path=$(xcode-select -p)
 
@@ -132,7 +138,7 @@ export CPPFLAGS="-DICONV_CONST="
 export CFLAGS="-F$xcode_path/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks -framework Carbon -framework Foundation -framework CoreServices -framework SystemConfiguration -Wno-unused-command-line-argument -Wno-error=incompatible-function-pointer-types -fpermissive -Wno-error=unguarded-availability"
 export CXXFLAGS="-F$xcode_path/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks -framework Carbon -framework Foundation -framework CoreServices -framework SystemConfiguration -Wno-unused-command-line-argument -Wno-error=unguarded-availability"
 export OBJCXXFLAGS="-F$xcode_path/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks -framework Carbon -framework Foundation -framework CoreServices -framework SystemConfiguration -Wno-unused-command-line-argument -Wno-error=unguarded-availability"
-export LDFLAGS="-L\"\$BUILD_ROOT/root/lib\" -L$xcode_path/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/lib -F$xcode_path/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks -framework Carbon -framework Foundation -framework CoreServices -framework SystemConfiguration -Wno-unused-command-line-argument -Wl,-no_compact_unwind"
+export LDFLAGS="-L\"\$BUILD_ROOT/root/lib\" -L$xcode_path/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/lib -F$xcode_path/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks -framework Carbon -framework Foundation -framework CoreServices -framework SystemConfiguration -Wno-unused-command-line-argument -Wl,-no_compact_unwind $rt_lib"
 
 export UUID_CFLAGS="-I\"\$BUILD_ROOT/root/stow/libuuid/include\""
 export UUID_LIBS="-L\"\$BUILD_ROOT/root/stow/libuuid/lib\" -luuid"