diff --git a/lix/libexpr/eval.cc b/lix/libexpr/eval.cc
index 4303e4b70..232614be1 100644
--- a/lix/libexpr/eval.cc
+++ b/lix/libexpr/eval.cc
@@ -4,6 +4,7 @@
 #include "lix/libutil/archive.hh"
 #include "lix/libutil/ansicolor.hh"
 #include "lix/libutil/async.hh"
+#include "lix/libutil/current-process.hh"
 #include "lix/libutil/deprecated-features.hh"
 #include "lix/libutil/error.hh"
 #include "lix/libutil/english.hh"
@@ -391,6 +392,11 @@ Evaluator::Evaluator(
 box_ptr<EvalState> Evaluator::begin(AsyncIoRoot & aio)
 {
     assert(!activeEval);
+
+    // Increase the default stack size for the evaluator and for
+    // libstdc++'s std::regex.
+    ensureStackSizeAtLeast(64ul * 1024 * 1024);
+
     return box_ptr<EvalState>::unsafeFromNonnull(
         std::unique_ptr<EvalState>(new EvalState(aio, *this))
     );
diff --git a/lix/libutil/current-process.cc b/lix/libutil/current-process.cc
index 0c9df5b89..816f96061 100644
--- a/lix/libutil/current-process.cc
+++ b/lix/libutil/current-process.cc
@@ -54,8 +54,12 @@ unsigned int getMaxCPU()
 
 rlim_t savedStackSize = 0;
 
-void setStackSize(rlim_t stackSize)
+void ensureStackSizeAtLeast(rlim_t stackSize)
 {
+    if (savedStackSize >= stackSize) {
+        return;
+    }
+
     struct rlimit limit;
     if (getrlimit(RLIMIT_STACK, &limit) == 0 && limit.rlim_cur < stackSize) {
         savedStackSize = limit.rlim_cur;
diff --git a/lix/libutil/current-process.hh b/lix/libutil/current-process.hh
index 316af234e..42c952de9 100644
--- a/lix/libutil/current-process.hh
+++ b/lix/libutil/current-process.hh
@@ -14,12 +14,10 @@ namespace nix {
  */
 unsigned int getMaxCPU();
 
-
 /**
- * Change the stack size.
+ * Increase the stack size rlimit if it is currently smaller than `stackSize`.
  */
-void setStackSize(rlim_t stackSize);
-
+void ensureStackSizeAtLeast(rlim_t stackSize);
 
 /**
  * Restore the original inherited Unix process context (such as signal
diff --git a/lix/nix/main.cc b/lix/nix/main.cc
index 77e38ee97..3057ff223 100644
--- a/lix/nix/main.cc
+++ b/lix/nix/main.cc
@@ -665,10 +665,6 @@ int main(int argc, char * * argv)
         std::abort();
     }
 
-    // Increase the default stack size for the evaluator and for
-    // libstdc++'s std::regex.
-    nix::setStackSize(64ul * 1024 * 1024);
-
     return nix::handleExceptions(argv[0], [&]() {
         nix::AsyncIoRoot aio;
         return nix::mainWrapped(aio, argc, argv);
diff --git a/subprojects/nix-eval-jobs/src/worker.cc b/subprojects/nix-eval-jobs/src/worker.cc
index 29db4fa89..9910a1db2 100644
--- a/subprojects/nix-eval-jobs/src/worker.cc
+++ b/subprojects/nix-eval-jobs/src/worker.cc
@@ -127,7 +127,7 @@ void worker(nix::AutoCloseFD &to, nix::AutoCloseFD &from, MyArgs &args)
 try {
     // Increase the default stack size for the evaluator and for
     // libstdc++'s std::regex.
-    nix::setStackSize(64 * 1024 * 1024);
+    nix::ensureStackSizeAtLeast(64 * 1024 * 1024);
 
 #if HAVE_BOEHMGC
     // We are doing the garbage collection by killing forks.