diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index cf4b375ce00..dcb975aaa66 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -218,6 +218,61 @@ jobs:
         export OMP_NUM_THREADS=1
         mpirun -n 2 Examples/Physics_applications/laser_acceleration/PICMI_inputs_3d.py
 
+  build_UB_sanitizer:
+    name: Clang UB sanitizer
+    runs-on: ubuntu-22.04
+    if: github.event.pull_request.draft == false
+    env:
+      CC: clang
+      CXX: clang++
+      # On CI for this test, Ninja is slower than the default:
+      #CMAKE_GENERATOR: Ninja
+    steps:
+    - uses: actions/checkout@v4
+    - name: install dependencies
+      run: |
+        .github/workflows/dependencies/clang15.sh
+    - name: CCache Cache
+      uses: actions/cache@v4
+      with:
+        path: ~/.cache/ccache
+        key: ccache-${{ github.workflow }}-${{ github.job }}-git-${{ github.sha }}
+        restore-keys: |
+             ccache-${{ github.workflow }}-${{ github.job }}-git-
+    - name: build WarpX
+      run: |
+        export CCACHE_COMPRESS=1
+        export CCACHE_COMPRESSLEVEL=10
+        export CCACHE_MAXSIZE=100M
+        ccache -z
+
+        export CXX=$(which clang++-15)
+        export CC=$(which clang-15)
+        export CXXFLAGS="-fsanitize=undefined -fno-sanitize-recover=all"
+
+        cmake -S . -B build                 \
+          -GNinja                           \
+          -DCMAKE_VERBOSE_MAKEFILE=ON       \
+          -DWarpX_DIMS="RZ;1;2;3"           \
+          -DWarpX_PSATD=ON                  \
+          -DWarpX_QED=ON                    \
+          -DWarpX_QED_TABLE_GEN=ON          \
+          -DWarpX_OPENPMD=ON                \
+          -DWarpX_PRECISION=SINGLE          \
+          -DWarpX_PARTICLE_PRECISION=SINGLE
+        cmake --build build -j 4
+
+        ccache -s
+        du -hs ~/.cache/ccache
+
+    - name: run with UB sanitizer
+      run: |
+        export OMP_NUM_THREADS=2
+        mpirun -n 2 ./build/bin/warpx.rz Examples/Physics_applications/laser_acceleration/inputs_rz
+        mpirun -n 2 ./build/bin/warpx.1d Examples/Physics_applications/laser_acceleration/inputs_1d
+        mpirun -n 2 ./build/bin/warpx.2d Examples/Physics_applications/laser_acceleration/inputs_2d
+        mpirun -n 2 ./build/bin/warpx.3d Examples/Physics_applications/laser_acceleration/inputs_3d
+
   save_pr_number:
     if: github.event_name == 'pull_request'
     runs-on: ubuntu-latest
diff --git a/Source/Diagnostics/ReducedDiags/FieldProbeParticleContainer.cpp b/Source/Diagnostics/ReducedDiags/FieldProbeParticleContainer.cpp
index 7e7aecb9167..dc26de3c1e6 100644
--- a/Source/Diagnostics/ReducedDiags/FieldProbeParticleContainer.cpp
+++ b/Source/Diagnostics/ReducedDiags/FieldProbeParticleContainer.cpp
@@ -76,6 +76,10 @@ FieldProbeParticleContainer::AddNParticles (int lev,
 
     // number of particles to add
     auto const np = static_cast<int>(x.size());
+    if (np <= 0){
+        Redistribute();
+        return;
+    }
 
     // have to resize here, not in the constructor because grids have not
     // been built when constructor was called.
@@ -122,8 +126,8 @@ FieldProbeParticleContainer::AddNParticles (int lev,
     pinned_tile.push_back_real(FieldProbePIdx::Bz, np, 0.0);
     pinned_tile.push_back_real(FieldProbePIdx::S, np, 0.0);
 
-    auto old_np = particle_tile.numParticles();
-    auto new_np = old_np + pinned_tile.numParticles();
+    const auto old_np = particle_tile.numParticles();
+    const auto new_np = old_np + pinned_tile.numParticles();
     particle_tile.resize(new_np);
     amrex::copyParticles(
         particle_tile, pinned_tile, 0, old_np, pinned_tile.numParticles());