diff --git a/.github/workflows/header-only-test.yml b/.github/workflows/header-only-test.yml
index d91c48fe0b..5c5e855b4d 100644
--- a/.github/workflows/header-only-test.yml
+++ b/.github/workflows/header-only-test.yml
@@ -24,7 +24,7 @@ jobs:
 
     - name: Run CMake
       run: |
-        cmake -B build -S header-only -DCMAKE_RUNTIME_OUTPUT_DIRECTORY=bin -DCMAKE_BUILD_TYPE=Release -DBUILD_TESTS=ON
+        cmake -B build -S header-only -DCMAKE_RUNTIME_OUTPUT_DIRECTORY=bin -DCMAKE_BUILD_TYPE=Debug -DBUILD_TESTS=ON
         cmake --build build/
 
     - name: Run tests
diff --git a/header-only/tests/test_1494-layout-builder.cpp b/header-only/tests/test_1494-layout-builder.cpp
index c9c6201fef..3a58c24ca7 100644
--- a/header-only/tests/test_1494-layout-builder.cpp
+++ b/header-only/tests/test_1494-layout-builder.cpp
@@ -1275,7 +1275,7 @@ test_IndexedOption() {
 
   double data[3] = {3.3, 4.4, 5.5};
 
-  builder.extend_valid(3);
+  builder.extend_valid(1);
   subbuilder.extend(data, 3);
 
   builder.extend_invalid(2);