diff --git a/scripts/install-multi-user.sh b/scripts/install-multi-user.sh
index 13762cba3..35341543e 100644
--- a/scripts/install-multi-user.sh
+++ b/scripts/install-multi-user.sh
@@ -567,7 +567,7 @@ install_from_extracted_nix() {
         cd "$EXTRACTED_NIX_PATH"
 
         _sudo "to copy the basic Nix files to the new store at $NIX_ROOT/store" \
-              rsync -rlpt ./store/* "$NIX_ROOT/store/"
+              rsync -rlpt --chmod=-w ./store/* "$NIX_ROOT/store/"
 
         if [ -d "$NIX_INSTALLED_NIX" ]; then
             echo "      Alright! We have our first nix at $NIX_INSTALLED_NIX"
diff --git a/scripts/install.in b/scripts/install.in
index 4500fd54a..6709f00d4 100644
--- a/scripts/install.in
+++ b/scripts/install.in
@@ -36,6 +36,7 @@ tarball="$tmpDir/$(basename "$tmpDir/nix-@nixVersion@-$system.tar.xz")"
 
 require_util curl "download the binary tarball"
 require_util tar "unpack the binary tarball"
+require_util xz "unpack the binary tarball"
 
 echo "downloading Nix @nixVersion@ binary tarball for $system from '$url' to '$tmpDir'..."
 curl -L "$url" -o "$tarball" || oops "failed to download '$url'"
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index a8945996e..7e97f3c22 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -20,13 +20,6 @@ namespace nix {
    must be deleted and recreated on startup.) */
 #define DEFAULT_SOCKET_PATH "/daemon-socket/socket"
 
-/* chroot-like behavior from Apple's sandbox */
-#if __APPLE__
-    #define DEFAULT_ALLOWED_IMPURE_PREFIXES "/System/Library /usr/lib /dev /bin/sh"
-#else
-    #define DEFAULT_ALLOWED_IMPURE_PREFIXES ""
-#endif
-
 Settings settings;
 
 static GlobalConfig::Register r1(&settings);
@@ -68,7 +61,12 @@ Settings::Settings()
     sandboxPaths = tokenizeString<StringSet>("/bin/sh=" SANDBOX_SHELL);
 #endif
 
-    allowedImpureHostPrefixes = tokenizeString<StringSet>(DEFAULT_ALLOWED_IMPURE_PREFIXES);
+
+/* chroot-like behavior from Apple's sandbox */
+#if __APPLE__
+    sandboxPaths = tokenizeString<StringSet>("/System/Library/Frameworks /System/Library/PrivateFrameworks /bin/sh /bin/bash /private/tmp /private/var/tmp /usr/lib");
+    allowedImpureHostPrefixes = tokenizeString<StringSet>("/System/Library /usr/lib /dev /bin/sh");
+#endif
 }
 
 void loadConfFile()
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index d0500be22..41bbed33f 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -311,12 +311,7 @@ public:
     Setting<bool> printMissing{this, true, "print-missing",
         "Whether to print what paths need to be built or downloaded."};
 
-    Setting<std::string> preBuildHook{this,
-#if __APPLE__
-        nixLibexecDir + "/nix/resolve-system-dependencies",
-#else
-        "",
-#endif
+    Setting<std::string> preBuildHook{this, "",
         "pre-build-hook",
         "A program to run just before a build to set derivation-specific build settings."};
 
diff --git a/src/libstore/sandbox-defaults.sb b/src/libstore/sandbox-defaults.sb
index 0299d1ee4..351037822 100644
--- a/src/libstore/sandbox-defaults.sb
+++ b/src/libstore/sandbox-defaults.sb
@@ -71,6 +71,12 @@
        (literal "/dev/zero")
        (subpath "/dev/fd"))
 
+; Allow pseudo-terminals.
+(allow file*
+       (literal "/dev/ptmx")
+       (regex #"^/dev/pty[a-z]+")
+       (regex #"^/dev/ttys[0-9]+"))
+
 ; Does nothing, but reduces build noise.
 (allow file* (literal "/dev/dtracehelper"))
 
@@ -85,3 +91,7 @@
        (literal "/etc")
        (literal "/var")
        (literal "/private/var/tmp"))
+
+; This is used by /bin/sh on macOS 10.15 and later.
+(allow file*
+       (literal "/private/var/select/sh"))