diff --git a/.github/workflows/nightly.yml b/.github/workflows/nightly.yml
index 0609fef70..641a354f0 100644
--- a/.github/workflows/nightly.yml
+++ b/.github/workflows/nightly.yml
@@ -6,6 +6,7 @@ on:
   workflow_dispatch:
   schedule:
     - cron: '0 4 * * *'
+  pull_request:
 
 permissions:
   contents: read
diff --git a/.github/workflows/pr_push.yml b/.github/workflows/pr_push.yml
index fffdc7373..633fbe7c9 100644
--- a/.github/workflows/pr_push.yml
+++ b/.github/workflows/pr_push.yml
@@ -6,7 +6,7 @@ on:
   push:
     branches-ignore:
       - 'dependabot/**'
-  pull_request:
+  # pull_request:
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
diff --git a/CMakeLists.txt b/CMakeLists.txt
index fe6599d6c..8d4a6118a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -329,7 +329,25 @@ if(UMF_LINK_HWLOC_STATICALLY)
         # ./configure invocation below, so hwloc would otherwise be built with
         # the ambient host compiler instead of the one CMake was configured to
         # use (e.g. a sysroot- or toolchain-file-pinned compiler), causing an
-        # ABI mismatch against the rest of the build.
+        # ABI mismatch against the rest of the build. CC/CXX are passed as
+        # space-separated "compiler [flags...]" strings (like CC="ccache gcc"),
+        # so --sysroot/--gcc-toolchain can be appended directly; make
+        # word-splits them unquoted when invoking the compiler.
+        set(UMF_HWLOC_CC "${CMAKE_C_COMPILER}")
+        set(UMF_HWLOC_CXX "${CMAKE_CXX_COMPILER}")
+        if(CMAKE_SYSROOT)
+            string(APPEND UMF_HWLOC_CC " --sysroot=${CMAKE_SYSROOT}")
+            string(APPEND UMF_HWLOC_CXX " --sysroot=${CMAKE_SYSROOT}")
+        endif()
+        if(CMAKE_C_COMPILER_EXTERNAL_TOOLCHAIN)
+            string(APPEND UMF_HWLOC_CC
+                   " --gcc-toolchain=${CMAKE_C_COMPILER_EXTERNAL_TOOLCHAIN}")
+        endif()
+        if(CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN)
+            string(APPEND UMF_HWLOC_CXX
+                   " --gcc-toolchain=${CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN}")
+        endif()
+
         ExternalProject_Add(
             hwloc_targ
             PREFIX ${hwloc_targ_PREFIX}
@@ -338,11 +356,11 @@ if(UMF_LINK_HWLOC_STATICALLY)
             UPDATE_DISCONNECTED TRUE
             PATCH_COMMAND git apply
                           ${PROJECT_SOURCE_DIR}/cmake/fix_coverity_issues.patch
-            CONFIGURE_COMMAND ${CMAKE_COMMAND} -E env CC=${CMAKE_C_COMPILER}
-                              CXX=${CMAKE_CXX_COMPILER} <SOURCE_DIR>/autogen.sh
+            CONFIGURE_COMMAND ${CMAKE_COMMAND} -E env "CC=${UMF_HWLOC_CC}"
+                              "CXX=${UMF_HWLOC_CXX}" <SOURCE_DIR>/autogen.sh
             COMMAND
-                ${CMAKE_COMMAND} -E env CC=${CMAKE_C_COMPILER}
-                CXX=${CMAKE_CXX_COMPILER} <SOURCE_DIR>/configure
+                ${CMAKE_COMMAND} -E env "CC=${UMF_HWLOC_CC}"
+                "CXX=${UMF_HWLOC_CXX}" <SOURCE_DIR>/configure
                 --prefix=<INSTALL_DIR> --enable-static=yes --enable-shared=no
                 --disable-libxml2 --disable-pci --disable-levelzero
                 --disable-opencl --disable-cuda --disable-nvml --disable-libudev