diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 88c516546..9069d9b06 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -2774,10 +2774,10 @@ void DerivationGoal::runChild()
                     sandboxProfile += "(deny default (with no-log))\n";
                 }
 
-                sandboxProfile += "(import \"sandbox-defaults.sb\")";
+                sandboxProfile += "(import \"sandbox-defaults.sb\")\n";
 
                 if (fixedOutput)
-                    sandboxProfile += "(import \"sandbox-network.sb\")";
+                    sandboxProfile += "(import \"sandbox-network.sb\")\n";
 
                 /* Our rwx outputs */
                 sandboxProfile += "(allow file-read* file-write* process-exec\n";
@@ -2820,7 +2820,7 @@ void DerivationGoal::runChild()
 
                 sandboxProfile += additionalSandboxProfile;
             } else
-                sandboxProfile += "(import \"sandbox-minimal.sb\")";
+                sandboxProfile += "(import \"sandbox-minimal.sb\")\n";
 
             debug("Generated sandbox profile:");
             debug(sandboxProfile);
@@ -2829,6 +2829,8 @@ void DerivationGoal::runChild()
 
             writeFile(sandboxFile, sandboxProfile);
 
+            bool allowLocalNetworking = get(drv->env, "__darwinAllowLocalNetworking") == "1";
+
             /* The tmpDir in scope points at the temporary build directory for our derivation. Some packages try different mechanisms
                to find temporary directories, so we want to open up a broader place for them to dump their files, if needed. */
             Path globalTmpDir = canonPath(getEnv("TMPDIR", "/tmp"), true);
@@ -2844,6 +2846,10 @@ void DerivationGoal::runChild()
             args.push_back("_GLOBAL_TMP_DIR=" + globalTmpDir);
             args.push_back("-D");
             args.push_back("IMPORT_DIR=" + settings.nixDataDir + "/nix/sandbox/");
+            if (allowLocalNetworking) {
+                args.push_back("-D");
+                args.push_back(string("_ALLOW_LOCAL_NETWORKING=1"));
+            }
             args.push_back(drv->builder);
         }
 #endif
diff --git a/src/libstore/sandbox-defaults.sb b/src/libstore/sandbox-defaults.sb
index d63c8f813..cf700c62c 100644
--- a/src/libstore/sandbox-defaults.sb
+++ b/src/libstore/sandbox-defaults.sb
@@ -30,6 +30,29 @@
 ; Without this line clang cannot write to /dev/null, breaking some configure tests.
 (allow file-read-metadata (literal "/dev"))
 
+; Many packages like to do local networking in their test suites, but let's only
+; allow it if the package explicitly asks for it.
+(if (param "_ALLOW_LOCAL_NETWORKING")
+    (begin
+      (allow network* (local ip) (local tcp) (local udp))
+
+      ; Allow access to /etc/resolv.conf (which is a symlink to
+      ; /private/var/run/resolv.conf).
+      ; TODO: deduplicate with sandbox-network.sb
+      (allow file-read-metadata
+             (literal "/var")
+             (literal "/etc")
+             (literal "/etc/resolv.conf")
+             (literal "/private/etc/resolv.conf"))
+
+      (allow file-read*
+             (literal "/private/var/run/resolv.conf"))
+
+      ; Allow DNS lookups. This is even needed for localhost, which lots of tests rely on
+      (allow file-read-metadata (literal "/etc/hosts"))
+      (allow file-read*         (literal "/private/etc/hosts"))
+      (allow network-outbound (remote unix-socket (path-literal "/private/var/run/mDNSResponder")))))
+
 ; Standard devices.
 (allow file*
        (literal "/dev/null")
@@ -54,5 +77,4 @@
 (allow file-read-metadata
        (literal "/etc")
        (literal "/var")
-       (literal "/private/var/tmp")
-       )
+       (literal "/private/var/tmp"))