diff --git a/examples/benchmarks/input_output/interleave_promises.effekt b/examples/benchmarks/input_output/interleave_promises.effekt
index 1363530ff..ffc10fc56 100644
--- a/examples/benchmarks/input_output/interleave_promises.effekt
+++ b/examples/benchmarks/input_output/interleave_promises.effekt
@@ -23,11 +23,11 @@ def run(n: Int) = {
     promise(box {
       with on[IOError].result
       val filename = foldername ++ i.show ++ ".txt"
-      val file = open(filename, WriteOnly())
+      val file = openForWriting(filename)
       val buffer = bytearray(size, 35.toByte)
       repeat(8) {
-        val i = write(file, buffer, 0, size, -1)
-        if (i < size) {
+        val m = write(file, buffer, 0, size, -1)
+        if (m < buffer.size) {
           panic("failed write")
         }
       }
@@ -38,11 +38,11 @@ def run(n: Int) = {
   promises.foreachIndex { (i, p) =>
     p.await().value()
     val filename = foldername ++ i.show ++ ".txt"
-    val file = open(filename, ReadOnly())
+    val file = openForReading(filename)
     val buffer = bytearray::allocate(size)
     repeat(8) {
-      val i = read(file, buffer, 0, size, -1)
-      if (i < size) {
+      val m = read(file, buffer, 0, size, -1)
+      if (m < buffer.size) {
         panic("failed read")
       }
     }
diff --git a/examples/benchmarks/input_output/large_file.effekt b/examples/benchmarks/input_output/large_file.effekt
index 278b8c2e2..ec450d3a6 100644
--- a/examples/benchmarks/input_output/large_file.effekt
+++ b/examples/benchmarks/input_output/large_file.effekt
@@ -6,33 +6,38 @@ import io/filesystem
 
 
 def run(n: Int) = {
-  with on[IOError].panic;
 
   val filename = "/tmp/large_file.txt"
   val size = 4096
 
   val _ = {
-    val file = open(filename, WriteOnly())
+    val file = internal::openForWriting(filename)
+    if (file < 0) {
+      panic("failed open for writing")
+    }
     val outputBuffer = bytearray(size, 33.toByte)
     outputBuffer.unsafeSet(999, 10.toByte)
     repeat(n) {
-      val i = write(file, outputBuffer, 0, size, -1)
-      if (i < size) {
+      val m = internal::write(file, outputBuffer, 0, size, -1)
+      if (m < outputBuffer.size) {
         panic("failed write")
       }
     }
-    close(file)
+    internal::close(file)
   }
 
-  val file = open(filename, ReadOnly())
+  val file = internal::openForReading(filename)
+  if (file < 0) {
+    panic("failed open for reading")
+  }
   val inputBuffer = bytearray::allocate(size)
   repeat(n) {
-    val i = read(file, inputBuffer, 0, size, -1)
-    if (i < size) {
+    val m = internal::read(file, inputBuffer, 0, size, -1)
+    if (m < inputBuffer.size) {
       panic("failed read")
     }
   }
-  close(file)
+  internal::close(file)
 
   return 0
 }
diff --git a/examples/benchmarks/input_output/small_files.effekt b/examples/benchmarks/input_output/small_files.effekt
index 1638b8608..32e2acf86 100644
--- a/examples/benchmarks/input_output/small_files.effekt
+++ b/examples/benchmarks/input_output/small_files.effekt
@@ -6,34 +6,42 @@ import io/filesystem
 
 
 def run(n: Int) = {
-  with on[IOError].panic;
 
   val foldername = "/tmp/small_files/"
   val size = 4096
 
-  on[IOError].result { mkdir(foldername) } match {
-    case Error(EEXIST(), msg) => ()
-    case Error(e, m) => do raise(e, m)
-    case Success(()) => ()
+  val code = internal::mkdir(foldername)
+  if (code < 0 && code != -17) {
+    panic("failed to make directory")
   }
 
   val buffer = bytearray(size, 33.toByte)
   each(0, n) { i =>
     val filename = foldername ++ i.show ++ ".txt"
-    val file = open(filename, WriteOnly())
-    if (write(file, buffer, 0, size, -1) < size) {
+    val file = internal::openForWriting(filename)
+    if (file < 0) {
+      panic("failed open for writing")
+    }
+    val m = internal::write(file, buffer, 0, size, -1)
+    if (m < buffer.size) {
       panic("failed write")
     }
-    close(file)
+    val _ = internal::close(file)
+    ()
   }
 
   each(0, n) { i =>
     val filename = foldername ++ i.show ++ ".txt"
-    val file = open(filename, ReadOnly())
-    if (read(file, buffer, 0, size, -1) < size) {
+    val file = internal::openForReading(filename)
+    if (file < 0) {
+      panic("failed open for reading")
+    }
+    val m = internal::read(file, buffer, 0, size, -1)
+    if (m < buffer.size) {
       panic("failed read")
     }
-    close(file)
+    val _ = internal::close(file)
+    ()
   }
 
   return 0
diff --git a/libraries/llvm/io.c b/libraries/llvm/io.c
index 3383ecd5c..1d17b38f5 100644
--- a/libraries/llvm/io.c
+++ b/libraries/llvm/io.c
@@ -71,7 +71,7 @@ void c_fs_open(String path, int flags, Stack stack) {
     uv_fs_t* request = malloc(sizeof(uv_fs_t));
     request->data = stack;
 
-    int result = uv_fs_open(uv_default_loop(), request, path_str, flags, 0666, c_resume_int_fs);
+    int result = uv_fs_open(uv_default_loop(), request, path_str, flags, 0777, c_resume_int_fs);
 
     if (result < 0) {
         uv_fs_req_cleanup(request);
@@ -157,7 +157,7 @@ void c_fs_mkdir(String path, Stack stack) {
     request->data = stack;
 
     // Perform the mkdir operation
-    int result = uv_fs_mkdir(uv_default_loop(), request, path_str, 0666, c_resume_int_fs);
+    int result = uv_fs_mkdir(uv_default_loop(), request, path_str, 0777, c_resume_int_fs);
 
     if (result < 0) {
         uv_fs_req_cleanup(request);