diff --git a/lix/libfetchers/git.cc b/lix/libfetchers/git.cc
index 3231ec011..aa3ef7150 100644
--- a/lix/libfetchers/git.cc
+++ b/lix/libfetchers/git.cc
@@ -22,6 +22,7 @@
 #include <string.h>
 #include <sys/time.h>
 #include <sys/wait.h>
+#include <unistd.h>
 
 using namespace std::string_literals;
 
@@ -164,11 +165,19 @@ WorkdirInfo getWorkdirInfo(const Input & input, const Path & workdir)
 
     /* Check whether HEAD points to something that looks like a commit,
        since that is the refrence we want to use later on. */
-    auto result = runProgram(RunOptions {
+    auto result = runProgram(RunOptions{
         .program = "git",
-        .args = { "-C", workdir, "--git-dir", gitDir, "rev-parse", "--verify", "--no-revs", "HEAD^{commit}" },
+        .args =
+            {"-C",
+             workdir,
+             "--git-dir",
+             gitDir,
+             "rev-parse",
+             "--verify",
+             "--no-revs",
+             "HEAD^{commit}"},
         .environment = env,
-        .mergeStderrToStdout = true
+        .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}},
     });
     auto exitCode = WEXITSTATUS(result.first);
     auto errorMessage = result.second;
@@ -709,10 +718,12 @@ struct GitInputScheme : InputScheme
         AutoDelete delTmpDir(tmpDir, true);
         PathFilter filter = defaultPathFilter;
 
-        auto result = runProgram(RunOptions {
+        auto result = runProgram(RunOptions{
             .program = "git",
-            .args = { "-C", repoDir, "--git-dir", gitDir, "cat-file", "commit", input.getRev()->gitRev() },
-            .mergeStderrToStdout = true
+            .args =
+                {"-C", repoDir, "--git-dir", gitDir, "cat-file", "commit", input.getRev()->gitRev()
+                },
+            .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}},
         });
         if (WEXITSTATUS(result.first) == 128
             && result.second.find("bad file") != std::string::npos)
diff --git a/lix/libstore/build/derivation-goal.cc b/lix/libstore/build/derivation-goal.cc
index 69e654490..48d38ffb4 100644
--- a/lix/libstore/build/derivation-goal.cc
+++ b/lix/libstore/build/derivation-goal.cc
@@ -891,7 +891,7 @@ void runPostBuildHook(
         .program = settings.postBuildHook,
         .environment = hookEnvironment,
         .captureStdout = true,
-        .mergeStderrToStdout = true,
+        .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}},
     });
     Finally const _wait([&] {
         try {
diff --git a/lix/libstore/globals.cc b/lix/libstore/globals.cc
index 9221da32b..b4328b068 100644
--- a/lix/libstore/globals.cc
+++ b/lix/libstore/globals.cc
@@ -242,9 +242,17 @@ StringSet Settings::getDefaultExtraPlatforms()
     // machines. Note that we can’t force processes from executing
     // x86_64 in aarch64 environments or vice versa since they can
     // always exec with their own binary preferences.
-    if (std::string{SYSTEM} == "aarch64-darwin" &&
-        runProgram(RunOptions {.program = "arch", .args = {"-arch", "x86_64", "/usr/bin/true"}, .mergeStderrToStdout = true}).first == 0)
+    if (std::string{SYSTEM} == "aarch64-darwin"
+        && runProgram(RunOptions{
+                          .program = "arch",
+                          .args = {"-arch", "x86_64", "/usr/bin/true"},
+                          .redirections = {{.from = STDERR_FILENO, .to = STDOUT_FILENO}}
+                      }
+           ).first
+            == 0)
+    {
         extraPlatforms.insert("x86_64-darwin");
+    }
 #endif
 
     return extraPlatforms;
diff --git a/lix/libstore/ssh.cc b/lix/libstore/ssh.cc
index b43cc50a9..2b329f231 100644
--- a/lix/libstore/ssh.cc
+++ b/lix/libstore/ssh.cc
@@ -8,6 +8,7 @@
 #include "lix/libutil/strings.hh"
 #include "lix/libstore/temporary-dir.hh"
 #include <sys/socket.h>
+#include <unistd.h>
 
 namespace nix {
 
diff --git a/lix/libutil/processes.cc b/lix/libutil/processes.cc
index 6b24d943f..0dcd96ba9 100644
--- a/lix/libutil/processes.cc
+++ b/lix/libutil/processes.cc
@@ -330,9 +330,11 @@ RunningProgram runProgram2(const RunOptions & options)
             replaceEnv(*options.environment);
         if (options.captureStdout && dup2(out.writeSide.get(), STDOUT_FILENO) == -1)
             throw SysError("dupping stdout");
-        if (options.mergeStderrToStdout)
-            if (dup2(STDOUT_FILENO, STDERR_FILENO) == -1)
-                throw SysError("cannot dup stdout into stderr");
+        for (auto redirection : options.redirections) {
+            if (dup2(redirection.to, redirection.from) == -1) {
+                throw SysError("dupping fd %i to %i", redirection.from, redirection.to);
+            }
+        }
 
         if (options.chdir && chdir((*options.chdir).c_str()) == -1)
             throw SysError("chdir failed");
diff --git a/lix/libutil/processes.hh b/lix/libutil/processes.hh
index 01c42b9fc..3311b8fb8 100644
--- a/lix/libutil/processes.hh
+++ b/lix/libutil/processes.hh
@@ -76,6 +76,11 @@ std::string runProgram(Path program, bool searchPath = false,
 
 struct RunOptions
 {
+    struct Redirection
+    {
+        int from, to;
+    };
+
     Path program;
     bool searchPath = true;
     Strings args = {};
@@ -84,8 +89,8 @@ struct RunOptions
     std::optional<Path> chdir = {};
     std::optional<std::map<std::string, std::string>> environment = {};
     bool captureStdout = false;
-    bool mergeStderrToStdout = false;
     bool isInteractive = false;
+    std::vector<Redirection> redirections;
 };
 
 struct [[nodiscard("you must call RunningProgram::wait()")]] RunningProgram