diff --git a/core/libs/prx/libc/src/StandardStreams.cpp b/core/libs/prx/libc/src/StandardStreams.cpp
index 32837f9cf..856937ab4 100644
--- a/core/libs/prx/libc/src/StandardStreams.cpp
+++ b/core/libs/prx/libc/src/StandardStreams.cpp
@@ -78,6 +78,10 @@ int APS5_VABI fileno_nid_postfix(FileStream* stream) {
 int APS5_VABI setvbuf_nid_postfix(FileStream* stream, char* buffer, int mode, std::size_t size) {
     if (mode < 0 || mode > 2) return -1;
     const int native = mode == 0 ? _IOFBF : mode == 1 ? _IOLBF : _IONBF;
+    if (native != _IONBF && size == 0) {
+        buffer = nullptr;
+        size = BUFSIZ;
+    }
     return std::setvbuf(GetNativeStream(stream), buffer, native, size);
 }
 void APS5_VABI setbuf_nid_postfix(FileStream* stream, char* buffer) {
diff --git a/core/libs/tests/GuestStandardStreams.cpp b/core/libs/tests/GuestStandardStreams.cpp
index 714912017..99f344536 100644
--- a/core/libs/tests/GuestStandardStreams.cpp
+++ b/core/libs/tests/GuestStandardStreams.cpp
@@ -180,6 +180,10 @@ int main() {
     Require(&guest == &stream.GuestState());
     Require(guest.position == nullptr && guest.readRemaining == 0 && guest.writeRemaining == 0);
     Require(guest.descriptor == fileno_nid_postfix(&stream));
+    FileStream lineBuffered(std::tmpfile());
+    Require(setvbuf_nid_postfix(&lineBuffered, nullptr, 1, 0) == 0);
+    FileStream fullyBuffered(std::tmpfile());
+    Require(setvbuf_nid_postfix(&fullyBuffered, nullptr, 0, 0) == 0);
     Require(setvbuf_nid_postfix(&stream, nullptr, 2, 0) == 0);
     Require(fputc_nid_postfix('A', &stream) == 'A');
     Require(--guest.writeRemaining < 0 && __swbuf_nid_postfix('\n', &stream) == '\n');