diff --git a/CMakeLists.txt b/CMakeLists.txt
index d10d9cd75d33..067d756210cd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -576,7 +576,7 @@ if (BUILD_SPARSE)
         GPU_TARGETS=${CMAKE_HIP_ARCHITECTURES}
         CMAKE_C_COMPILER=${CMAKE_C_COMPILER}
         CMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
-        CMAKE_PREFIX_PATH=${CMAKE_PREFIX_PATH}
+        CMAKE_PREFIX_PATH="${CMAKE_PREFIX_PATH}"
         CMAKE_HIP_ARCHITECTURES=${CMAKE_HIP_ARCHITECTURES}
         BINDIR=${CMAKE_CURRENT_BINARY_DIR}
         INCLUDEDIR="${DGL_INCLUDE_DIRS}"
@@ -641,7 +641,6 @@ if (BUILD_GRAPHBOLT)
         PYTORCH_ROCM_ARCH=${CMAKE_HIP_ARCHITECTURES}
         CMAKE_C_COMPILER=${CMAKE_C_COMPILER}
         CMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
-        CMAKE_PREFIX_PATH=${CMAKE_PREFIX_PATH}
         GPU_TARGETS=${CMAKE_HIP_ARCHITECTURES}
         CMAKE_HIP_ARCHITECTURES=${CMAKE_HIP_ARCHITECTURES}
         USE_HIP=${USE_HIP}
diff --git a/dgl_sparse/build.sh b/dgl_sparse/build.sh
index 96e4ad8dd5a6..2e574e76bb82 100644
--- a/dgl_sparse/build.sh
+++ b/dgl_sparse/build.sh
@@ -21,12 +21,19 @@ if [ -n "$CMAKE_CXX_COMPILER" ]; then
   CMAKE_COMPILER_FLAGS="$CMAKE_COMPILER_FLAGS -DCMAKE_CXX_COMPILER=$CMAKE_CXX_COMPILER"
 fi
 
-# Use CMAKE_PREFIX_PATH from parent if provided (helps find ROCm components)
+# Use CMAKE_PREFIX_PATH from parent if provided (helps find ROCm components).
+# CMake's add_custom_target converts semicolons to spaces; convert back for -D flag.
 CMAKE_PREFIX_FLAGS=""
 if [ -n "$CMAKE_PREFIX_PATH" ]; then
-  CMAKE_PREFIX_FLAGS="-DCMAKE_PREFIX_PATH=$CMAKE_PREFIX_PATH"
+  CMAKE_PREFIX_SEMICOLON="${CMAKE_PREFIX_PATH// /;}"
+  CMAKE_PREFIX_FLAGS="-DCMAKE_PREFIX_PATH=${CMAKE_PREFIX_SEMICOLON}"
 fi
 
+# Unset CFLAGS/CXXFLAGS inherited from parent — they contain -Werror which
+# breaks CMake's FindOpenMP test compilation.
+unset CFLAGS
+unset CXXFLAGS
+
 if [ "$USE_CUDA" = 'ON' ]; then
   CMAKE_FLAGS="-DCUDA_TOOLKIT_ROOT_DIR=$CUDA_TOOLKIT_ROOT_DIR -DTORCH_CUDA_ARCH_LIST=$TORCH_CUDA_ARCH_LIST -DUSE_CUDA=$USE_CUDA -DEXTERNAL_DMLC_LIB_PATH=$EXTERNAL_DMLC_LIB_PATH"
 elif [ "$USE_HIP" = 'ON' ]; then
diff --git a/graphbolt/build_rocm.sh b/graphbolt/build_rocm.sh
index c21ed190b11c..3b1467e0f67d 100644
--- a/graphbolt/build_rocm.sh
+++ b/graphbolt/build_rocm.sh
@@ -27,12 +27,19 @@ if [ -n "$CMAKE_CXX_COMPILER" ]; then
   CMAKE_COMPILER_FLAGS="$CMAKE_COMPILER_FLAGS -DCMAKE_CXX_COMPILER=$CMAKE_CXX_COMPILER"
 fi
 
-# Use CMAKE_PREFIX_PATH from parent if provided (helps find ROCm components)
+# Use CMAKE_PREFIX_PATH from parent if provided (helps find ROCm components).
+# CMake's add_custom_target converts semicolons to spaces; convert back for -D flag.
 CMAKE_PREFIX_FLAGS=""
 if [ -n "$CMAKE_PREFIX_PATH" ]; then
-  CMAKE_PREFIX_FLAGS="-DCMAKE_PREFIX_PATH=$CMAKE_PREFIX_PATH"
+  CMAKE_PREFIX_SEMICOLON="${CMAKE_PREFIX_PATH// /;}"
+  CMAKE_PREFIX_FLAGS="-DCMAKE_PREFIX_PATH=${CMAKE_PREFIX_SEMICOLON}"
 fi
 
+# Unset CFLAGS/CXXFLAGS inherited from parent — they contain -Werror which
+# breaks CMake's FindOpenMP test compilation. Graphbolt sets its own flags via Torch.
+unset CFLAGS
+unset CXXFLAGS
+
 CMAKE_FLAGS="-DCMAKE_EXPORT_COMPILE_COMMANDS=ON                                \
 -DCMAKE_HIP_ARCHITECTURES=${CMAKE_HIP_ARCHITECTURES}                           \
 -DUSE_HIP=$USE_HIP                                                             \