diff --git a/lix/libcmd/repl.hh b/lix/libcmd/repl.hh
index 0e24ba573..1a04bc5b9 100644
--- a/lix/libcmd/repl.hh
+++ b/lix/libcmd/repl.hh
@@ -2,10 +2,11 @@
 ///@file
 
 #include "lix/libexpr/eval.hh"
+#include "lix/libutil/types.hh"
 
 namespace nix {
 
-struct AbstractNixRepl
+struct AbstractNixRepl : NeverAsync
 {
     typedef std::vector<std::pair<Value*,std::string>> AnnotatedValues;
 
diff --git a/lix/libexpr/eval-error.cc b/lix/libexpr/eval-error.cc
index 62165ff4b..c8254a7be 100644
--- a/lix/libexpr/eval-error.cc
+++ b/lix/libexpr/eval-error.cc
@@ -1,6 +1,7 @@
 #include "lix/libexpr/eval-error.hh"
 #include "lix/libexpr/eval.hh"
 #include "lix/libexpr/value.hh"
+#include "lix/libutil/types.hh"
 
 namespace nix {
 
@@ -72,7 +73,7 @@ EvalErrorBuilder<T>::addTrace(PosIdx pos, std::string_view formatString, const A
 }
 
 template<class T>
-void EvalErrorBuilder<T>::debugThrow() &&
+void EvalErrorBuilder<T>::debugThrow(NeverAsync) &&
 {
     if (debug) {
         if (auto last = debug->traces().next()) {
diff --git a/lix/libexpr/eval-error.hh b/lix/libexpr/eval-error.hh
index 8e1a7c25e..2d010293c 100644
--- a/lix/libexpr/eval-error.hh
+++ b/lix/libexpr/eval-error.hh
@@ -91,7 +91,7 @@ public:
     /**
      * Throw the underlying exception, invoking the debug state callback.
      */
-    [[gnu::noinline, gnu::noreturn]] void debugThrow() &&;
+    [[gnu::noinline, gnu::noreturn]] void debugThrow(NeverAsync = {}) &&;
 
     /**
      * Throw the underlying exception, bypassing the debug state callback.
diff --git a/lix/libexpr/eval.cc b/lix/libexpr/eval.cc
index 95ba6023f..490759924 100644
--- a/lix/libexpr/eval.cc
+++ b/lix/libexpr/eval.cc
@@ -1,5 +1,6 @@
 #include "lix/libexpr/eval.hh"
 #include "lix/libexpr/eval-settings.hh"
+#include "lix/libstore/path.hh"
 #include "lix/libutil/archive.hh"
 #include "lix/libutil/ansicolor.hh"
 #include "lix/libutil/async.hh"
@@ -337,7 +338,7 @@ Evaluator::Evaluator(
           debugRepl ? std::make_unique<DebugState>(
               positions,
               symbols,
-              [this, debugRepl](const ValMap & extraEnv) {
+              [this, debugRepl](const ValMap & extraEnv, NeverAsync) {
                   return activeEval
                       ? debugRepl(*activeEval, extraEnv)
                       : ReplExitStatus::Continue;
@@ -731,7 +732,9 @@ public:
     }
 };
 
-void DebugState::onEvalError(const EvalError * error, const Env & env, const Expr & expr)
+void DebugState::onEvalError(
+    const EvalError * error, const Env & env, const Expr & expr, NeverAsync
+)
 {
     // Make sure we have a debugger to run and we're not already in a debugger.
     if (inDebugger)
@@ -765,7 +768,7 @@ void DebugState::onEvalError(const EvalError * error, const Env & env, const Exp
     if (se) {
         auto vm = mapStaticEnvBindings(symbols, *se.get(), env);
         DebuggerGuard _guard(inDebugger);
-        auto exitStatus = errorCallback(*vm);
+        auto exitStatus = errorCallback(*vm, {});
         switch (exitStatus) {
             case ReplExitStatus::QuitAll:
                 if (error)
@@ -2458,7 +2461,7 @@ std::pair<SingleDerivedPath, std::string_view> EvalState::coerceToSingleDerivedP
         [&](NixStringContextElem::DrvDeep &&) -> SingleDerivedPath {
             ctx.errors.make<EvalError>(
                 "string '%s' has a context which refers to a complete source and binary closure. This is not supported at this time",
-                s).withTrace(pos, errorCtx).debugThrow();
+                s).withTrace(pos, errorCtx).debugThrow(always_progresses);
         },
         [&](NixStringContextElem::Built && b) -> SingleDerivedPath {
             return std::move(b);
@@ -2484,13 +2487,13 @@ SingleDerivedPath EvalState::coerceToSingleDerivedPath(const PosIdx pos, Value &
                 ctx.errors.make<EvalError>(
                     "path string '%s' has context with the different path '%s'",
                     s, sExpected)
-                    .withTrace(pos, errorCtx).debugThrow();
+                    .withTrace(pos, errorCtx).debugThrow(always_progresses);
             },
             [&](const SingleDerivedPath::Built & b) {
                 ctx.errors.make<EvalError>(
                     "string '%s' has context with the output '%s' from derivation '%s', but the string is not the right placeholder for this derivation output. It should be '%s'",
                     s, b.output, b.drvPath->to_string(*ctx.store), sExpected)
-                    .withTrace(pos, errorCtx).debugThrow();
+                    .withTrace(pos, errorCtx).debugThrow(always_progresses);
             }
         }, derivedPath.raw());
     }
diff --git a/lix/libexpr/eval.hh b/lix/libexpr/eval.hh
index de8d715dd..5b70fcbcb 100644
--- a/lix/libexpr/eval.hh
+++ b/lix/libexpr/eval.hh
@@ -7,6 +7,7 @@
 #include "lix/libutil/box_ptr.hh"
 #include "lix/libutil/generator.hh"
 #include "lix/libutil/async.hh"
+#include "lix/libutil/source-path.hh"
 #include "lix/libutil/types.hh"
 #include "lix/libexpr/value.hh"
 #include "lix/libexpr/nixexpr.hh"
@@ -149,7 +150,7 @@ private:
     const SymbolTable & symbols;
 
 public:
-    std::function<ReplExitStatus(ValMap const & extraEnv)> errorCallback;
+    std::function<ReplExitStatus(ValMap const & extraEnv, NeverAsync)> errorCallback;
     bool stop = false;
     bool inDebugger = false;
     std::map<const Expr *, const std::shared_ptr<const StaticEnv>> exprEnvs;
@@ -158,7 +159,7 @@ public:
     explicit DebugState(
         const PosTable & positions,
         const SymbolTable & symbols,
-        std::function<ReplExitStatus(ValMap const & extraEnv)> errorCallback
+        std::function<ReplExitStatus(ValMap const & extraEnv, NeverAsync)> errorCallback
     )
         : positions(positions)
         , symbols(symbols)
@@ -167,7 +168,7 @@ public:
         assert(errorCallback);
     }
 
-    void onEvalError(const EvalError * error, const Env & env, const Expr & expr);
+    void onEvalError(const EvalError * error, const Env & env, const Expr & expr, NeverAsync = {});
 
     const std::shared_ptr<const StaticEnv> staticEnvFor(const Expr & expr) const
     {
@@ -469,7 +470,7 @@ public:
                 overloaded{
                     [](T & p) -> T { return std::move(p); },
                     [](EvalErrorBuilder<E> & e) -> T {
-                        std::move(e).debugThrow();
+                        std::move(e).debugThrow(always_progresses);
                     }
                 },
                 static_cast<std::variant<T, EvalErrorBuilder<E>> &>(*this)
diff --git a/lix/libexpr/primops.cc b/lix/libexpr/primops.cc
index be6b7baf1..21265f7f3 100644
--- a/lix/libexpr/primops.cc
+++ b/lix/libexpr/primops.cc
@@ -19,6 +19,7 @@
 #include "lix/libexpr/primops.hh"
 #include "lix/libfetchers/fetch-to-store.hh"
 #include "lix/libutil/result.hh"
+#include "lix/libutil/types.hh"
 
 #include <boost/container/small_vector.hpp>
 #include <kj/async.h>
@@ -50,7 +51,7 @@ StringMap EvalState::realiseContext(const NixStringContext & context)
     for (auto & c : context) {
         auto ensureValid = [&](const StorePath & p) {
             if (!aio.blockOn(ctx.store->isValidPath(p)))
-                ctx.errors.make<InvalidPathError>(ctx.store->printStorePath(p)).debugThrow();
+                ctx.errors.make<InvalidPathError>(ctx.store->printStorePath(p)).debugThrow(always_progresses);
         };
         std::visit(overloaded {
             [&](const NixStringContextElem::Built & b) {
@@ -432,7 +433,7 @@ template<typename Callable>
     }
 }
 
-struct CompareValues
+struct CompareValues : NeverAsync
 {
     EvalState & state;
     const PosIdx pos;
@@ -827,7 +828,7 @@ drvName, Bindings * attrs, Value & v)
         const std::string & key = state.ctx.symbols[i->name];
         vomit("processing attribute '%1%'", key);
 
-        auto handleHashMode = [&](const std::string_view s) {
+        auto handleHashMode = [&](const std::string_view s, NeverAsync = {}) {
             if (s == "recursive") ingestionMethod = FileIngestionMethod::Recursive;
             else if (s == "flat") ingestionMethod = FileIngestionMethod::Flat;
             else if (s == "text") {
@@ -839,7 +840,7 @@ drvName, Bindings * attrs, Value & v)
                 ).atPos(v).debugThrow();
         };
 
-        auto handleOutputs = [&](const Strings & ss) {
+        auto handleOutputs = [&](const Strings & ss, NeverAsync = {}) {
             outputs.clear();
             for (auto & j : ss) {
                 if (outputs.find(j) != outputs.end())
diff --git a/lix/libexpr/primops/context.cc b/lix/libexpr/primops/context.cc
index a5038a0f2..603368501 100644
--- a/lix/libexpr/primops/context.cc
+++ b/lix/libexpr/primops/context.cc
@@ -3,6 +3,7 @@
 #include "lix/libexpr/extra-primops.hh"
 #include "lix/libstore/derivations.hh"
 #include "lix/libstore/store-api.hh"
+#include "lix/libutil/types.hh"
 
 namespace nix {
 
@@ -69,7 +70,7 @@ void prim_addDrvOutputDependencies(EvalState & state, const PosIdx pos, Value *
                     state.ctx.errors.make<EvalError>(
                         "path '%s' is not a derivation",
                         state.ctx.store->printStorePath(c.path)
-                    ).atPos(pos).debugThrow();
+                    ).atPos(pos).debugThrow(always_progresses);
                 }
                 return NixStringContextElem::DrvDeep {
                     .drvPath = c.path,
@@ -79,7 +80,7 @@ void prim_addDrvOutputDependencies(EvalState & state, const PosIdx pos, Value *
                 state.ctx.errors.make<EvalError>(
                     "`addDrvOutputDependencies` can only act on derivations, not on a derivation output such as '%1%'",
                     c.output
-                ).atPos(pos).debugThrow();
+                ).atPos(pos).debugThrow(always_progresses);
             },
             [&](const NixStringContextElem::DrvDeep & c) -> NixStringContextElem::DrvDeep {
                 /* Reuse original item because we want this to be idempotent. */
diff --git a/lix/nix/eval.cc b/lix/nix/eval.cc
index 25ebcbe25..60b41823f 100644
--- a/lix/nix/eval.cc
+++ b/lix/nix/eval.cc
@@ -7,6 +7,7 @@
 #include "lix/libexpr/eval-inline.hh"
 #include "lix/libexpr/value-to-json.hh"
 #include "eval.hh"
+#include "lix/libutil/types.hh"
 
 namespace nix {
 
@@ -80,9 +81,9 @@ struct CmdEval : MixJSON, InstallableCommand, MixReadOnlyOption
             if (pathExists(*writeTo))
                 throw Error("path '%s' already exists", *writeTo);
 
-            std::function<void(Value & v, const PosIdx pos, const Path & path)> recurse;
+            std::function<void(Value & v, const PosIdx pos, const Path & path, NeverAsync)> recurse;
 
-            recurse = [&](Value & v, const PosIdx pos, const Path & path)
+            recurse = [&](Value & v, const PosIdx pos, const Path & path, NeverAsync)
             {
                 state->forceValue(v, pos);
                 if (v.type() == nString)
@@ -96,7 +97,7 @@ struct CmdEval : MixJSON, InstallableCommand, MixReadOnlyOption
                         try {
                             if (name == "." || name == "..")
                                 throw Error("invalid file name '%s'", name);
-                            recurse(*attr.value, attr.pos, concatStrings(path, "/", name));
+                            recurse(*attr.value, attr.pos, concatStrings(path, "/", name), {});
                         } catch (Error & e) {
                             e.addTrace(
                                 evaluator->positions[attr.pos],
@@ -109,7 +110,7 @@ struct CmdEval : MixJSON, InstallableCommand, MixReadOnlyOption
                     evaluator->errors.make<TypeError>("value at '%s' is not a string or an attribute set", evaluator->positions[pos]).debugThrow();
             };
 
-            recurse(*v, pos, *writeTo);
+            recurse(*v, pos, *writeTo, {});
         }
 
         else if (raw) {
diff --git a/lix/nix/flake.cc b/lix/nix/flake.cc
index 7884bc8ad..65d0c138b 100644
--- a/lix/nix/flake.cc
+++ b/lix/nix/flake.cc
@@ -19,6 +19,7 @@
 #include "lix/libutil/terminal.hh"
 #include "lix/libutil/signals.hh"
 #include "flake.hh"
+#include "lix/libutil/types.hh"
 
 #include <limits>
 #include <iomanip>
@@ -1194,13 +1195,15 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
             eval_cache::AttrCursor & visitor,
             const std::vector<std::string> & attrPath,
             const std::string & headerPrefix,
-            const std::string & nextPrefix)> visit;
+            const std::string & nextPrefix,
+            NeverAsync)> visit;
 
         visit = [&](
             eval_cache::AttrCursor & visitor,
             const std::vector<std::string> & attrPath,
             const std::string & headerPrefix,
-            const std::string & nextPrefix)
+            const std::string & nextPrefix,
+            NeverAsync)
             -> JSON
         {
             auto j = JSON::object();
@@ -1209,7 +1212,7 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                 fmt("evaluating '%s'", concatStringsSep(".", attrPath)));
 
             try {
-                auto recurse = [&]()
+                auto recurse = [&](NeverAsync = {})
                 {
                     if (!json)
                         logger->cout("%s", headerPrefix);
@@ -1226,12 +1229,12 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
                         attrPath2.push_back(attr);
                         auto j2 = visit(*visitor2, attrPath2,
                             fmt(ANSI_GREEN "%s%s" ANSI_NORMAL ANSI_BOLD "%s" ANSI_NORMAL, nextPrefix, last ? treeLast : treeConn, attr),
-                            nextPrefix + (last ? treeNull : treeLine));
+                            nextPrefix + (last ? treeNull : treeLine), {});
                         if (json) j.emplace(attr, std::move(j2));
                     }
                 };
 
-                auto showDerivation = [&]()
+                auto showDerivation = [&](NeverAsync = {})
                 {
                     auto name = visitor.getAttr(*state, "name")->getString(*state);
                     std::optional<std::string> description;
@@ -1410,7 +1413,7 @@ struct CmdFlakeShow : FlakeCommand, MixJSON
 
         auto cache = openEvalCache(*evaluator, flake);
 
-        auto j = visit(*cache->getRoot(), {}, fmt(ANSI_BOLD "%s" ANSI_NORMAL, flake->flake.lockedRef), "");
+        auto j = visit(*cache->getRoot(), {}, fmt(ANSI_BOLD "%s" ANSI_NORMAL, flake->flake.lockedRef), "", {});
         if (json)
             logger->cout("%s", j.dump());
     }
diff --git a/subprojects/nix-eval-jobs/src/worker.cc b/subprojects/nix-eval-jobs/src/worker.cc
index feaef7955..7fd66155d 100644
--- a/subprojects/nix-eval-jobs/src/worker.cc
+++ b/subprojects/nix-eval-jobs/src/worker.cc
@@ -89,7 +89,7 @@ readConstituents(const nix::Value *v, nix::box_ptr<nix::EvalState> &state,
             state->ctx.errors
                 .make<nix::EvalError>("derivation must have a ‘constituents’ "
                                       "attribute")
-                .debugThrow();
+                .debugThrow(nix::always_progresses); // we can't have a debugger here
 
         nix::NixStringContext context;
         state->coerceToString(a->pos, *a->value, context,
diff --git a/tests/unit/libcmd/args.cc b/tests/unit/libcmd/args.cc
index 3fd98cdc4..a9c0f4ed4 100644
--- a/tests/unit/libcmd/args.cc
+++ b/tests/unit/libcmd/args.cc
@@ -10,6 +10,7 @@
 #include "lix/libstore/filetransfer.hh"
 #include "lix/libmain/shared.hh"
 #include "lix/libstore/store-api.hh"
+#include "lix/libutil/types.hh"
 
 constexpr std::string_view INVALID_CHANNEL = "channel:example";
 constexpr std::string_view CHANNEL_URL = "https://nixos.org/channels/example/nixexprs.tar.xz";
diff --git a/tests/unit/libexpr/error_traces.cc b/tests/unit/libexpr/error_traces.cc
index 6b98c9014..2d2b2acc1 100644
--- a/tests/unit/libexpr/error_traces.cc
+++ b/tests/unit/libexpr/error_traces.cc
@@ -1,6 +1,7 @@
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 
+#include "lix/libutil/types.hh"
 #include "tests/libexpr.hh"
 
 namespace nix {
@@ -12,19 +13,23 @@ namespace nix {
 
     TEST_F(ErrorTraceTest, TraceBuilder) {
         ASSERT_THROW(
-            evaluator.errors.make<EvalError>("puppy").debugThrow(),
+            evaluator.errors.make<EvalError>("puppy").debugThrow(always_progresses),
             EvalError
         );
 
         ASSERT_THROW(
-            evaluator.errors.make<EvalError>("puppy").withTrace(noPos, "doggy").debugThrow(),
+            evaluator.errors.make<EvalError>("puppy")
+                .withTrace(noPos, "doggy")
+                .debugThrow(always_progresses),
             EvalError
         );
 
         ASSERT_THROW(
             try {
                 try {
-                    evaluator.errors.make<EvalError>("puppy").withTrace(noPos, "doggy").debugThrow();
+                    evaluator.errors.make<EvalError>("puppy")
+                        .withTrace(noPos, "doggy")
+                        .debugThrow(always_progresses);
                 } catch (Error & e) {
                     e.addTrace(evaluator.positions[noPos], "beans");
                     throw;
@@ -47,10 +52,12 @@ namespace nix {
 
     TEST_F(ErrorTraceTest, NestedThrows) {
         try {
-            evaluator.errors.make<EvalError>("puppy").withTrace(noPos, "doggy").debugThrow();
+            evaluator.errors.make<EvalError>("puppy")
+                .withTrace(noPos, "doggy")
+                .debugThrow(always_progresses);
         } catch (BaseError & e) {
             try {
-                evaluator.errors.make<EvalError>("beans").debugThrow();
+                evaluator.errors.make<EvalError>("beans").debugThrow(always_progresses);
             } catch (Error & e2) {
                 e.addTrace(evaluator.positions[noPos], "beans2");
                 //e2.addTrace(state.positions[noPos], "Something", "");