diff --git a/Tools/ci/build_all_runner.sh b/Tools/ci/build_all_runner.sh
index a47d42dd87..132b634ebd 100755
--- a/Tools/ci/build_all_runner.sh
+++ b/Tools/ci/build_all_runner.sh
@@ -3,6 +3,14 @@
 # Please only modify if you know what you are doing
 set -e
 
+# NuttX .o/.a live in the shared submodule trees, not per-board build dirs.
+# Wipe them between boards so stale objects from a prior board's defconfig
+# don't get linked into the next board's elf.
+clean_nuttx_state() {
+    git -C platforms/nuttx/NuttX/nuttx clean -dXf -q
+    git -C platforms/nuttx/NuttX/apps  clean -dXf -q
+}
+
 targets=$1
 for target in ${targets//,/ }
 do
@@ -14,4 +22,5 @@ do
     build_time="$(($diff /60/60))h $(($diff /60))m $(($diff % 60))s elapsed"
     echo -e "\033[0;32mBuild Time: [$build_time]"
     echo "::endgroup::"
+    clean_nuttx_state
 done
diff --git a/platforms/nuttx/NuttX/CMakeLists.txt b/platforms/nuttx/NuttX/CMakeLists.txt
index 3a700ce9ff..30182a722c 100644
--- a/platforms/nuttx/NuttX/CMakeLists.txt
+++ b/platforms/nuttx/NuttX/CMakeLists.txt
@@ -181,8 +181,15 @@ function(add_nuttx_dir nuttx_lib nuttx_lib_dir kernel extra target)
 		${CMAKE_CURRENT_SOURCE_DIR}/nuttx/${nuttx_lib_dir}/*.h
 	)
 
+	# Route kernel pass for mm/libc to kbin/; user pass uses bin/ for the
+	# same sources and would otherwise overwrite the kernel objects.
+	set(bindir_arg)
+	if(${kernel} STREQUAL y AND (${nuttx_lib_dir} STREQUAL mm OR ${nuttx_lib_dir} STREQUAL libs/libc))
+		set(bindir_arg BINDIR=kbin)
+	endif()
+
 	add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/nuttx/${nuttx_lib_dir}/lib${nuttx_lib}.a
-		COMMAND make -C ${nuttx_lib_dir} --no-print-directory --silent ${nuttx_lib_target} TOPDIR="${NUTTX_DIR}" KERNEL=${kernel} EXTRAFLAGS=${extra}
+		COMMAND make -C ${nuttx_lib_dir} --no-print-directory --silent ${nuttx_lib_target} TOPDIR="${NUTTX_DIR}" KERNEL=${kernel} EXTRAFLAGS=${extra} ${bindir_arg}
 		COMMAND ${CMAKE_COMMAND} -E copy_if_different ${NUTTX_DIR}/${nuttx_lib_dir}/lib${nuttx_lib}.a ${CMAKE_CURRENT_BINARY_DIR}/nuttx/${nuttx_lib_dir}/lib${nuttx_lib}.a
 		DEPENDS
 			${nuttx_lib_files}