diff --git a/src/libexpr/tests/value/context.cc b/src/libexpr/tests/value/context.cc
index 27d6920b0..0d9381577 100644
--- a/src/libexpr/tests/value/context.cc
+++ b/src/libexpr/tests/value/context.cc
@@ -95,13 +95,15 @@ Gen<NixStringContextElem::Built> Arbitrary<NixStringContextElem::Built>::arbitra
 
 Gen<NixStringContextElem> Arbitrary<NixStringContextElem>::arbitrary()
 {
-    switch (*gen::inRange<uint8_t>(0, 2)) {
+    switch (*gen::inRange<uint8_t>(0, std::variant_size_v<NixStringContextElem::Raw>)) {
     case 0:
         return gen::just<NixStringContextElem>(*gen::arbitrary<NixStringContextElem::Opaque>());
     case 1:
         return gen::just<NixStringContextElem>(*gen::arbitrary<NixStringContextElem::DrvDeep>());
-    default:
+    case 2:
         return gen::just<NixStringContextElem>(*gen::arbitrary<NixStringContextElem::Built>());
+    default:
+        assert(false);
     }
 }
 
diff --git a/src/libstore/tests/derived-path.cc b/src/libstore/tests/derived-path.cc
index e6d32dbd0..160443ec1 100644
--- a/src/libstore/tests/derived-path.cc
+++ b/src/libstore/tests/derived-path.cc
@@ -27,11 +27,13 @@ Gen<DerivedPath::Built> Arbitrary<DerivedPath::Built>::arbitrary()
 
 Gen<DerivedPath> Arbitrary<DerivedPath>::arbitrary()
 {
-    switch (*gen::inRange<uint8_t>(0, 1)) {
+    switch (*gen::inRange<uint8_t>(0, std::variant_size_v<DerivedPath::Raw>)) {
     case 0:
         return gen::just<DerivedPath>(*gen::arbitrary<DerivedPath::Opaque>());
-    default:
+    case 1:
         return gen::just<DerivedPath>(*gen::arbitrary<DerivedPath::Built>());
+    default:
+        assert(false);
     }
 }
 
diff --git a/src/libstore/tests/outputs-spec.cc b/src/libstore/tests/outputs-spec.cc
index 984d1d963..bf8deaa9d 100644
--- a/src/libstore/tests/outputs-spec.cc
+++ b/src/libstore/tests/outputs-spec.cc
@@ -206,15 +206,17 @@ using namespace nix;
 
 Gen<OutputsSpec> Arbitrary<OutputsSpec>::arbitrary()
 {
-    switch (*gen::inRange<uint8_t>(0, 1)) {
+    switch (*gen::inRange<uint8_t>(0, std::variant_size_v<OutputsSpec::Raw>)) {
     case 0:
         return gen::just((OutputsSpec) OutputsSpec::All { });
-    default:
+    case 1:
         return gen::just((OutputsSpec) OutputsSpec::Names {
             *gen::nonEmpty(gen::container<StringSet>(gen::map(
                 gen::arbitrary<StorePathName>(),
                 [](StorePathName n) { return n.name; }))),
         });
+    default:
+        assert(false);
     }
 }