diff --git a/src/lib/libfs.js b/src/lib/libfs.js
index af6f6f6728d43..a2da5eafcc6fb 100644
--- a/src/lib/libfs.js
+++ b/src/lib/libfs.js
@@ -1954,7 +1954,7 @@ FS.staticInit();`;
 for (let key in LibraryFS.$FS) {
   const alias = `$FS_${key}`;
   // Skip defining the alias if it already exists or if it's not an API function.
-  if (LibraryFS[alias] || key[0] !== key[0].toLowerCase()) {
+  if (LibraryFS[alias] || typeof LibraryFS.$FS[key] !== 'function' || key[0] !== key[0].toLowerCase()) {
     continue;
   }
   LibraryFS[alias] = `(...args) => FS.${key}(...args)`;
diff --git a/test/codesize/test_codesize_hello_O0.json b/test/codesize/test_codesize_hello_O0.json
index bb883c8e5b440..e4ee584222637 100644
--- a/test/codesize/test_codesize_hello_O0.json
+++ b/test/codesize/test_codesize_hello_O0.json
@@ -1,10 +1,10 @@
 {
-  "a.out.js": 23551,
-  "a.out.js.gz": 8559,
+  "a.out.js": 23395,
+  "a.out.js.gz": 8502,
   "a.out.nodebug.wasm": 14275,
   "a.out.nodebug.wasm.gz": 7098,
-  "total": 37826,
-  "total_gz": 15657,
+  "total": 37670,
+  "total_gz": 15600,
   "sent": [
     "fd_write"
   ],
diff --git a/test/codesize/test_codesize_minimal_O0.expected.js b/test/codesize/test_codesize_minimal_O0.expected.js
index 797b9905a86a5..e82c6c5015078 100644
--- a/test/codesize/test_codesize_minimal_O0.expected.js
+++ b/test/codesize/test_codesize_minimal_O0.expected.js
@@ -1023,16 +1023,6 @@ missingLibrarySymbols.forEach(missingLibrarySymbol)
   'FS_createDevice',
   'FS_readFile',
   'FS',
-  'FS_root',
-  'FS_mounts',
-  'FS_devices',
-  'FS_streams',
-  'FS_nextInode',
-  'FS_nameTable',
-  'FS_currentPath',
-  'FS_initialized',
-  'FS_ignorePermissions',
-  'FS_syncFSRequests',
   'FS_lookupPath',
   'FS_getPath',
   'FS_hashName',
@@ -1064,7 +1054,6 @@ missingLibrarySymbols.forEach(missingLibrarySymbol)
   'FS_closeStream',
   'FS_dupStream',
   'FS_doSetAttr',
-  'FS_chrdev_stream_ops',
   'FS_major',
   'FS_minor',
   'FS_makedev',
diff --git a/test/codesize/test_codesize_minimal_O0.json b/test/codesize/test_codesize_minimal_O0.json
index e52559434d575..497e2d8deb801 100644
--- a/test/codesize/test_codesize_minimal_O0.json
+++ b/test/codesize/test_codesize_minimal_O0.json
@@ -1,10 +1,10 @@
 {
-  "a.out.js": 18738,
-  "a.out.js.gz": 6730,
+  "a.out.js": 18582,
+  "a.out.js.gz": 6672,
   "a.out.nodebug.wasm": 1071,
   "a.out.nodebug.wasm.gz": 636,
-  "total": 19809,
-  "total_gz": 7366,
+  "total": 19653,
+  "total_gz": 7308,
   "sent": [],
   "imports": [],
   "exports": [
diff --git a/test/codesize/test_unoptimized_code_size.json b/test/codesize/test_unoptimized_code_size.json
index 20b14290502c3..49629a20e7232 100644
--- a/test/codesize/test_unoptimized_code_size.json
+++ b/test/codesize/test_unoptimized_code_size.json
@@ -1,16 +1,16 @@
 {
-  "hello_world.js": 53025,
-  "hello_world.js.gz": 16866,
+  "hello_world.js": 52814,
+  "hello_world.js.gz": 16807,
   "hello_world.wasm": 14275,
   "hello_world.wasm.gz": 7098,
   "no_asserts.js": 22074,
   "no_asserts.js.gz": 7847,
   "no_asserts.wasm": 11389,
   "no_asserts.wasm.gz": 5645,
-  "strict.js": 50155,
-  "strict.js.gz": 15884,
+  "strict.js": 49944,
+  "strict.js.gz": 15826,
   "strict.wasm": 14275,
   "strict.wasm.gz": 7096,
-  "total": 165193,
-  "total_gz": 60436
+  "total": 164771,
+  "total_gz": 60319
 }