diff --git a/.circleci/config.yml b/.circleci/config.yml
index 4c139e23b3abd..0159ba1da508b 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -590,6 +590,7 @@ jobs:
             wasmfs.test_readdir_rawfs
             wasmfs.test_utime
             wasmfs.test_unistd_unlink
+            wasmfs.test_unistd_dup
             wasmfs.test_unistd_access
             wasmfs.test_unistd_close
             wasmfs.test_unistd_truncate
diff --git a/system/lib/wasmfs/file_table.cpp b/system/lib/wasmfs/file_table.cpp
index ef11597dc2ac9..13b8429f40386 100644
--- a/system/lib/wasmfs/file_table.cpp
+++ b/system/lib/wasmfs/file_table.cpp
@@ -33,6 +33,7 @@ std::shared_ptr<DataFile>
 FileTable::Handle::setEntry(__wasi_fd_t fd,
                             std::shared_ptr<OpenFileState> openFile) {
   assert(fd >= 0);
+  assert(fd < WASMFS_FD_MAX);
   if (fd >= fileTable.entries.size()) {
     fileTable.entries.resize(fd + 1);
   }
@@ -50,7 +51,7 @@ FileTable::Handle::setEntry(__wasi_fd_t fd,
 __wasi_fd_t
 FileTable::Handle::addEntry(std::shared_ptr<OpenFileState> openFileState) {
   // TODO: add freelist to avoid linear lookup time.
-  for (__wasi_fd_t i = 0;; i++) {
+  for (__wasi_fd_t i = 0; i < WASMFS_FD_MAX; i++) {
     if (!getEntry(i)) {
       (void)setEntry(i, openFileState);
       return i;
diff --git a/system/lib/wasmfs/file_table.h b/system/lib/wasmfs/file_table.h
index 75eca96328a9c..e85d9b38e07f2 100644
--- a/system/lib/wasmfs/file_table.h
+++ b/system/lib/wasmfs/file_table.h
@@ -15,6 +15,9 @@
 #include <vector>
 #include <wasi/api.h>
 
+// Copied from legacy FS (FS.MAX_OPEN_FDS)
+#define WASMFS_FD_MAX 4096
+
 namespace wasmfs {
 static_assert(std::is_same<size_t, __wasi_size_t>::value,
               "size_t should be the same as __wasi_size_t");
diff --git a/system/lib/wasmfs/syscalls.cpp b/system/lib/wasmfs/syscalls.cpp
index f52eb65ad9ec2..48dd311c33c93 100644
--- a/system/lib/wasmfs/syscalls.cpp
+++ b/system/lib/wasmfs/syscalls.cpp
@@ -60,7 +60,7 @@ int __syscall_dup3(int oldfd, int newfd, int flags) {
   if (!oldOpenFile) {
     return -EBADF;
   }
-  if (newfd < 0) {
+  if (newfd < 0 || newfd >= WASMFS_FD_MAX) {
     return -EBADF;
   }
   if (oldfd == newfd) {
diff --git a/test/other/codesize/test_codesize_files_wasmfs.size b/test/other/codesize/test_codesize_files_wasmfs.size
index 16548dcf103a6..61a9d15a5ddbe 100644
--- a/test/other/codesize/test_codesize_files_wasmfs.size
+++ b/test/other/codesize/test_codesize_files_wasmfs.size
@@ -1 +1 @@
-49979
+49968
diff --git a/test/unistd/dup.c b/test/unistd/dup.c
index dcc737c3b819c..b276f608605ee 100644
--- a/test/unistd/dup.c
+++ b/test/unistd/dup.c
@@ -9,7 +9,6 @@
 #include <errno.h>
 #include <unistd.h>
 #include <fcntl.h>
-#include <emscripten.h>
 #include <assert.h>
 #include <string.h>
 
@@ -21,7 +20,7 @@ int main() {
   f = open("/", O_RDONLY);
   f2 = open("/", O_RDONLY);
   f3 = dup(f);
-  printf("errno: %d\n", errno);
+  printf("errno: %s\n", strerror(errno));
   assert(f != -1);
   assert(f2 != -1);
   assert(f3 != -1);
@@ -40,7 +39,7 @@ int main() {
   assert(f != -1);
   assert(f2 != -1);
   assert(f3 != -1);
-  printf("errno: %d\n", errno);
+  printf("errno: %s\n", strerror(errno));
   printf("f: %d\n", f != f2 && f != f3);
   printf("f2,f3: %d\n", f2 == f3);
   printf("close(f1): %d\n", close(f));
@@ -53,7 +52,7 @@ int main() {
   f = dup2(-2, -2);
   printf("f: %d\n", f);
   assert(f == -1);
-  printf("errno: %d\n", errno);
+  printf("errno: %s\n", strerror(errno));
   printf("close(f): %d\n", close(f));
   printf("\n");
   errno = 0;
@@ -64,11 +63,11 @@ int main() {
   f3 = dup2(f, -1);
   printf("f3: %d\n", f3);
   assert(f3 == -1);
-  printf("errno: %d\n", errno);
+  printf("errno: %s\n", strerror(errno));
   f3 = dup2(f, 256000);
   printf("f3: %d\n", f3);
   assert(f3 == -1);
-  printf("errno: %d\n", errno);
+  printf("errno: %s\n", strerror(errno));
   printf("close(f1): %d\n", close(f));
   printf("\n");
   errno = 0;
diff --git a/test/unistd/dup.out b/test/unistd/dup.out
index ed3f03e4d48d6..22ed73631cc11 100644
--- a/test/unistd/dup.out
+++ b/test/unistd/dup.out
@@ -1,5 +1,5 @@
 DUP
-errno: 0
+errno: No error information
 f: 1
 f2,f3: 1
 close(f1): 0
@@ -7,7 +7,7 @@ close(f2): 0
 close(f3): 0
 
 DUP2
-errno: 0
+errno: No error information
 f: 1
 f2,f3: 1
 close(f1): 0
@@ -16,14 +16,14 @@ close(f3): -1
 
 DUP2 bad fds
 f: -1
-errno: 8
+errno: Bad file descriptor
 close(f): -1
 
 DUP2 bad newfd
 f3: -1
-errno: 8
+errno: Bad file descriptor
 f3: -1
-errno: 8
+errno: Bad file descriptor
 close(f1): 0
 
 DUP2 pipe