diff --git a/fs/mmap/fs_rammap.c b/fs/mmap/fs_rammap.c
index 23e6ceb330d..d81832e2956 100644
--- a/fs/mmap/fs_rammap.c
+++ b/fs/mmap/fs_rammap.c
@@ -140,6 +140,12 @@ FAR void *rammap(int fd, size_t length, off_t offset)
 
   /* Allocate a region of memory of the specified size */
 
+  if ((unsigned int)fd >= CONFIG_NFILE_DESCRIPTORS)
+    {
+      errcode = EBADF;
+      goto errout;
+    }
+
   alloc = (FAR uint8_t *)kumm_malloc(sizeof(struct fs_rammap_s) + length);
   if (!alloc)
     {