diff --git a/libraries/AP_Filesystem/AP_Filesystem_ROMFS.cpp b/libraries/AP_Filesystem/AP_Filesystem_ROMFS.cpp
index f481d872558e5c..d4eca8812fb82f 100644
--- a/libraries/AP_Filesystem/AP_Filesystem_ROMFS.cpp
+++ b/libraries/AP_Filesystem/AP_Filesystem_ROMFS.cpp
@@ -32,6 +32,8 @@ int AP_Filesystem_ROMFS::open(const char *fname, int flags, bool allow_absolute_
         errno = EROFS;
         return -1;
     }
+
+    WITH_SEMAPHORE(record_sem); // search for free file record
     uint8_t idx;
     for (idx=0; idx<max_open_file; idx++) {
         if (file[idx].data == nullptr) {
@@ -42,10 +44,6 @@ int AP_Filesystem_ROMFS::open(const char *fname, int flags, bool allow_absolute_
         errno = ENFILE;
         return -1;
     }
-    if (file[idx].data != nullptr) {
-        errno = EBUSY;
-        return -1;
-    }
     file[idx].data = AP_ROMFS::find_decompress(fname, file[idx].size);
     if (file[idx].data == nullptr) {
         errno = ENOENT;
@@ -61,6 +59,8 @@ int AP_Filesystem_ROMFS::close(int fd)
         errno = EBADF;
         return -1;
     }
+
+    WITH_SEMAPHORE(record_sem); // release file record
     AP_ROMFS::free(file[fd].data);
     file[fd].data = nullptr;
     return 0;
@@ -142,6 +142,7 @@ int AP_Filesystem_ROMFS::mkdir(const char *pathname)
 
 void *AP_Filesystem_ROMFS::opendir(const char *pathname)
 {
+    WITH_SEMAPHORE(record_sem); // search for free directory record
     uint8_t idx;
     for (idx=0; idx<max_open_dir; idx++) {
         if (dir[idx].path == nullptr) {
@@ -216,6 +217,8 @@ int AP_Filesystem_ROMFS::closedir(void *dirp)
         errno = EBADF;
         return -1;
     }
+
+    WITH_SEMAPHORE(record_sem); // release directory record
     free(dir[idx].path);
     dir[idx].path = nullptr;
     return 0;
diff --git a/libraries/AP_Filesystem/AP_Filesystem_ROMFS.h b/libraries/AP_Filesystem/AP_Filesystem_ROMFS.h
index a5176aeaf44ba2..07fd2ca9888cb1 100644
--- a/libraries/AP_Filesystem/AP_Filesystem_ROMFS.h
+++ b/libraries/AP_Filesystem/AP_Filesystem_ROMFS.h
@@ -19,6 +19,8 @@
 
 #if AP_FILESYSTEM_ROMFS_ENABLED
 
+#include <AP_HAL/Semaphores.h>
+
 #include "AP_Filesystem_backend.h"
 
 class AP_Filesystem_ROMFS : public AP_Filesystem_Backend
@@ -56,6 +58,9 @@ class AP_Filesystem_ROMFS : public AP_Filesystem_Backend
     void unload_file(FileData *fd) override;
     
 private:
+    // protect searching for free file/dir records when opening/closing
+    HAL_Semaphore record_sem;
+
     // only allow up to 4 files at a time
     static constexpr uint8_t max_open_file = 4;
     static constexpr uint8_t max_open_dir = 4;