diff --git a/.github/workflows/build_and_test_compiler_zoo.yml b/.github/workflows/build_and_test_compiler_zoo.yml
index 7919a764..e28b3538 100644
--- a/.github/workflows/build_and_test_compiler_zoo.yml
+++ b/.github/workflows/build_and_test_compiler_zoo.yml
@@ -185,20 +185,20 @@ jobs:
     steps:
     - uses: actions/checkout@v4
 
-    - name: Setup Compiler 
+    - name: Setup Compiler
       shell: bash
       run: $GITHUB_WORKSPACE/.github/workflows/scripts/compiler_setup.sh gnu 12
 
     - name: Configure CMake
       shell: bash
       run: cmake -S $GITHUB_WORKSPACE -B ${{runner.workspace}}/build
-                 -DCMAKE_INSTALL_PREFIX=${{runner.workspace}}/install 
+                 -DCMAKE_INSTALL_PREFIX=${{runner.workspace}}/install
                  -DCMAKE_PREFIX_PATH=${ENV_PREFIX_PATH}
                  -DCMAKE_TOOLCHAIN_FILE=${GITHUB_WORKSPACE}/${GH_ACTIONS_TOOLCHAIN}
 
     - name: Build
       shell: bash
-      run: cmake --build ${{runner.workspace}}/build -j2 
+      run: cmake --build ${{runner.workspace}}/build -j2
 
     - name: Install
       shell: bash
@@ -206,10 +206,68 @@ jobs:
 
     - name: CMake Discovery Configure
       shell: bash
-      run: cmake -S $GITHUB_WORKSPACE/tests/cmake/discovery -B ${{runner.workspace}}/cmake_discovery_build 
+      run: cmake -S $GITHUB_WORKSPACE/tests/cmake/discovery -B ${{runner.workspace}}/cmake_discovery_build
                  -DCMAKE_PREFIX_PATH="${{runner.workspace}}/install;${ENV_PREFIX_PATH}"
                  -DCMAKE_TOOLCHAIN_FILE=${GITHUB_WORKSPACE}/${GH_ACTIONS_TOOLCHAIN}
 
     - name: CMake Discovery Build
       shell: bash
       run: cmake --build ${{runner.workspace}}/cmake_discovery_build -j2
+
+  macos_build:
+    name: macOS Build and Test
+    runs-on: macos-14
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - uses: mamba-org/setup-micromamba@v2
+      with:
+        environment-name: gauxc
+        create-args: >-
+          python=3.11
+          c-compiler
+          cxx-compiler
+          fortran-compiler
+          mpich
+          cmake
+          hdf5
+          openblas
+          ccache
+        init-shell: bash
+        cache-environment: true
+
+    - name: Setup ccache
+      shell: micromamba-shell {0}
+      run: |
+        ccache --set-config=max_size=2G
+        ccache --set-config=compression=true
+        echo "CMAKE_C_COMPILER_LAUNCHER=ccache" >> $GITHUB_ENV
+        echo "CMAKE_CXX_COMPILER_LAUNCHER=ccache" >> $GITHUB_ENV
+
+    - name: Restore ccache
+      uses: actions/cache@v4
+      with:
+        path: ~/.ccache
+        key: ccache-macos-${{ github.sha }}
+        restore-keys: |
+          ccache-macos-
+
+    - name: Build
+      shell: micromamba-shell {0}
+      run: |
+        cmake -S . -B build \
+          -DCMAKE_BUILD_TYPE=Release \
+          -DGAUXC_ENABLE_MPI=ON \
+          -DGAUXC_ENABLE_TESTS=ON \
+          -DBUILD_TESTING=ON \
+          -DCMAKE_POLICY_VERSION_MINIMUM=3.5
+        cmake --build build -j3
+
+    - name: ccache statistics
+      shell: micromamba-shell {0}
+      run: ccache --show-stats
+
+    - name: Test
+      shell: micromamba-shell {0}
+      run: ctest --test-dir build --output-on-failure
diff --git a/.gitignore b/.gitignore
index 65b35b0d..be531abc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,8 @@ src/xc_integrator/local_work_driver/host/obara_saika/generator/integral*
 src/xc_integrator/local_work_driver/host/obara_saika/generator/obara*
 src/xc_integrator/local_work_driver/host/obara_saika/generator/*.x
 *.swp
+
+# Build directories
+build/
+_build/
+cmake-build-*/
diff --git a/src/xc_integrator/integrator_util/spherical_harmonics.cxx b/src/xc_integrator/integrator_util/spherical_harmonics.cxx
index be7cf84a..bbc838e1 100644
--- a/src/xc_integrator/integrator_util/spherical_harmonics.cxx
+++ b/src/xc_integrator/integrator_util/spherical_harmonics.cxx
@@ -125,6 +125,10 @@ void scaled_ylm_new(const int lmax, const std::array<double, 3> x, const std::ar
 }
 
 // compute scaled spherical harmonics, with standard library functions
+// DISABLED ON MACOS: std::sph_legendre not available in Apple's libc++
+// This function is unused. Added in commit 66784a4 (Feb 2025), never called.
+// Production uses scaled_ylm_new() above.
+#ifndef __APPLE__
 std::vector<double> scaled_ylm_std(int lmax, std::array<double, 3> x, std::array<double, 3> a, double r) {
 
     std::vector<double> delta = {x[0] - a[0], x[1] - a[1], x[2] - a[2]};
@@ -155,6 +159,7 @@ std::vector<double> scaled_ylm_std(int lmax, std::array<double, 3> x, std::array
     }
     return ylm;
 }
+#endif // __APPLE__
 
 void scaled_ylm_matrix(const int lmax, const double* points, const int32_t  npts, const std::array<double, 3> center, const double radius, double* ylm_matrix) {
   int nharmonics = (lmax + 1) * (lmax + 1);