diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index c72b69af2..7520e95a9 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1098,7 +1098,7 @@ Value * ExprPath::maybeThunk(EvalState & state, Env & env)
 }
 
 
-void EvalState::evalFile(const SourcePath & path_, Value & v, bool mustBeTrivial)
+void EvalState::evalFile(const SourcePath & path_, Value & v)
 {
     auto path = checkSourcePath(path_);
 
@@ -1124,7 +1124,7 @@ void EvalState::evalFile(const SourcePath & path_, Value & v, bool mustBeTrivial
     if (!e)
         e = parseExprFromFile(checkSourcePath(resolvedPath));
 
-    cacheFile(path, resolvedPath, e, v, mustBeTrivial);
+    cacheFile(path, resolvedPath, e, v);
 }
 
 
@@ -1139,8 +1139,8 @@ void EvalState::cacheFile(
     const SourcePath & path,
     const SourcePath & resolvedPath,
     Expr * e,
-    Value & v,
-    bool mustBeTrivial)
+    Value & v
+)
 {
     fileParseCache[resolvedPath] = e;
 
@@ -1153,12 +1153,6 @@ void EvalState::cacheFile(
                 e->getPos() ? std::make_shared<Pos>(positions[e->getPos()]) : nullptr,
                 "while evaluating the file '%1%':", resolvedPath.to_string())
             : nullptr;
-
-        // Enforce that 'flake.nix' is a direct attrset, not a
-        // computation.
-        if (mustBeTrivial &&
-            !(dynamic_cast<ExprAttrs *>(e)))
-            error<EvalError>("file '%s' must be an attribute set", path).debugThrow();
         eval(e, v);
     } catch (Error & e) {
         addErrorTrace(e, "while evaluating the file '%1%':", resolvedPath.to_string());
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 411364d9f..04f8cc2c9 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -352,11 +352,9 @@ public:
     Expr * parseStdin();
 
     /**
-     * Evaluate an expression read from the given file to normal
-     * form. Optionally enforce that the top-level expression is
-     * trivial (i.e. doesn't require arbitrary computation).
+     * Evaluate an expression read from the given file to normal form.
      */
-    void evalFile(const SourcePath & path, Value & v, bool mustBeTrivial = false);
+    void evalFile(const SourcePath & path, Value & v);
 
     /**
      * Like `evalFile`, but with an already parsed expression.
@@ -365,8 +363,8 @@ public:
         const SourcePath & path,
         const SourcePath & resolvedPath,
         Expr * e,
-        Value & v,
-        bool mustBeTrivial = false);
+        Value & v
+    );
 
     void resetFileCache();
 
diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index ac50351ad..13cc29d4c 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -233,9 +233,13 @@ static Flake getFlake(
         .sourceInfo = std::make_shared<fetchers::Tree>(std::move(sourceInfo))
     };
 
-    // NOTE evalFile forces vInfo to be an attrset because mustBeTrivial is true.
     Value vInfo;
-    state.evalFile(CanonPath(flakeFile), vInfo, true); // FIXME: symlink attack
+    state.evalFile(CanonPath(flakeFile), vInfo); // FIXME: symlink attack
+    if (vInfo.type() != nAttrs) {
+        state.error<EvalError>(
+            "file '%s' must be an attribute set, but is %s", flakeFile, showType(vInfo)
+        ).debugThrow();
+    }
 
     if (auto description = vInfo.attrs->get(state.sDescription)) {
         expectType(state, nString, *description->value, description->pos);
diff --git a/tests/functional/flakes/trivial-flake.sh b/tests/functional/flakes/trivial-flake.sh
new file mode 100644
index 000000000..d30bcd6a0
--- /dev/null
+++ b/tests/functional/flakes/trivial-flake.sh
@@ -0,0 +1,45 @@
+# Allow trivial evaluation in flake metadata.
+source ./common.sh
+
+clearStore
+
+flakeLetDir="$TEST_ROOT/flake-let"
+flakeInterpDir="$TEST_ROOT/flake-interp"
+
+for flakeDir in "$flakeLetDir" "$flakeInterpDir"; do
+  mkdir -vp "$flakeDir"
+done
+
+# let is trivial; this should succeed
+cat > "$flakeLetDir/flake.nix" <<EOF
+let
+  description = "meow";
+in {
+  inherit description;
+  inputs = { };
+
+  outputs = { self }: {
+  };
+}
+EOF
+
+# string interpolation thunks; this should fail
+cat > "$flakeInterpDir/flake.nix" <<EOF
+let
+  lix-forgejo = "git+https://git.lix.systems";
+in {
+  inputs = {
+    lix.url = "\${lix-forgejo}/lix-project/lix";
+  };
+
+  outputs = { self, lix }: {
+  };
+}
+EOF
+
+(cd "$flakeLetDir" && nix flake show)
+
+(
+  cd "$flakeInterpDir"
+  expectStderr 1 nix flake show | grepQuiet "error: expected a string but got a thunk"
+)
diff --git a/tests/functional/meson.build b/tests/functional/meson.build
index a13dee001..567cc5c29 100644
--- a/tests/functional/meson.build
+++ b/tests/functional/meson.build
@@ -174,6 +174,7 @@ functional_tests_scripts = [
   'fetchClosure.sh',
   'completions.sh',
   'flakes/show.sh',
+  'flakes/trivial-flake.sh',
   'impure-derivations.sh',
   'path-from-hash-part.sh',
   'toString-path.sh',