diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 4cb43bc11..3fc156108 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -755,7 +755,6 @@ void LocalDerivationGoal::startBuilder()
     result.startTime = time(0);
 
     /* Fork a child to build the package. */
-    ProcessOptions options;
 
 #if __linux__
     if (useChroot) {
@@ -798,8 +797,6 @@ void LocalDerivationGoal::startBuilder()
 
         userNamespaceSync.create();
 
-        options.allowVfork = false;
-
         Path maxUserNamespaces = "/proc/sys/user/max_user_namespaces";
         static bool userNamespacesEnabled =
             pathExists(maxUserNamespaces)
@@ -857,7 +854,7 @@ void LocalDerivationGoal::startBuilder()
             writeFull(builderOut.writeSide.get(),
                 fmt("%d %d\n", usingUserNamespace, child));
             _exit(0);
-        }, options);
+        });
 
         int res = helper.wait();
         if (res != 0 && settings.sandboxFallback) {
@@ -921,10 +918,9 @@ void LocalDerivationGoal::startBuilder()
 #endif
     {
     fallback:
-        options.allowVfork = !buildUser && !drv->isBuiltin();
         pid = startProcess([&]() {
             runChild();
-        }, options);
+        });
     }
 
     /* parent */
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 0b261ca60..563a72c12 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -939,9 +939,6 @@ void killUser(uid_t uid)
        users to which the current process can send signals.  So we
        fork a process, switch to uid, and send a mass kill. */
 
-    ProcessOptions options;
-    options.allowVfork = false;
-
     Pid pid = startProcess([&]() {
 
         if (setuid(uid) == -1)
@@ -964,7 +961,7 @@ void killUser(uid_t uid)
         }
 
         _exit(0);
-    }, options);
+    });
 
     int status = pid.wait();
     if (status != 0)
@@ -1085,8 +1082,7 @@ void runProgram2(const RunOptions & options)
     // vfork implies that the environment of the main process and the fork will
     // be shared (technically this is undefined, but in practice that's the
     // case), so we can't use it if we alter the environment
-    if (options.environment)
-        processOptions.allowVfork = false;
+    processOptions.allowVfork = !options.environment;
 
     /* Fork. */
     Pid pid = startProcess([&]() {
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 6d3e64949..29232453f 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -262,7 +262,7 @@ struct ProcessOptions
     string errorPrefix = "";
     bool dieWithParent = true;
     bool runExitHandlers = false;
-    bool allowVfork = true;
+    bool allowVfork = false;
 };
 
 pid_t startProcess(std::function<void()> fun, const ProcessOptions & options = ProcessOptions());