diff --git a/core/libs/prx/libc/include/FileStream.hpp b/core/libs/prx/libc/include/FileStream.hpp
index 7a1b467be..9fff6280e 100644
--- a/core/libs/prx/libc/include/FileStream.hpp
+++ b/core/libs/prx/libc/include/FileStream.hpp
@@ -42,7 +42,7 @@ class FileStream {
     std::byte _reserved[256 - sizeof(GuestFilePrefix)]{};
     std::FILE* _handle;
     bool _dynamic;
-    bool encodingError = false;
+    bool guestError = false;
 
 public:
     explicit FileStream(std::FILE* handle, bool dynamic = false) : _handle(handle), _dynamic(dynamic) {
@@ -72,7 +72,7 @@ public:
     bool Reopen(const std::filesystem::path& filename, const char* mode) {
         auto* previous = GetHandle();
         _guest = {};
-        encodingError = false;
+        guestError = false;
 #ifdef _WIN32
         std::wstring wideMode;
         for (const char character : std::string_view(mode)) wideMode.push_back(static_cast<unsigned char>(character));
@@ -94,7 +94,7 @@ public:
         _guest.readRemaining = 0;
         _guest.writeRemaining = 0;
         _guest.flags = static_cast<std::int16_t>((_guest.flags & ~0x60) |
-            (std::feof(GetHandle()) ? 0x20 : 0) | (std::ferror(GetHandle()) || encodingError ? 0x40 : 0));
+            (std::feof(GetHandle()) ? 0x20 : 0) | (std::ferror(GetHandle()) || guestError ? 0x40 : 0));
     }
 
     void SyncUnlockedStatus() {
@@ -108,17 +108,17 @@ public:
         const bool error = ::ferror_unlocked(GetHandle()) != 0;
 #endif
         _guest.flags = static_cast<std::int16_t>((_guest.flags & ~0x60) |
-            (endOfFile ? 0x20 : 0) | (error || encodingError ? 0x40 : 0));
+            (endOfFile ? 0x20 : 0) | (error || guestError ? 0x40 : 0));
     }
 
-    void SetEncodingError() {
-        encodingError = true;
+    void SetError() {
+        guestError = true;
         SyncStatus();
     }
 
     void ClearError() {
         std::clearerr(GetHandle());
-        encodingError = false;
+        guestError = false;
         SyncStatus();
     }
 
diff --git a/core/libs/prx/libc/src/StandardStreams.cpp b/core/libs/prx/libc/src/StandardStreams.cpp
index 1d51cdb37..69e24de20 100644
--- a/core/libs/prx/libc/src/StandardStreams.cpp
+++ b/core/libs/prx/libc/src/StandardStreams.cpp
@@ -27,7 +27,7 @@ std::int32_t APS5_VABI ungetwc_nid_postfix(std::int32_t value, FileStream* strea
     if (value == -1) return -1;
     if (value < 0 || value > 255) {
         errno = 86;
-        stream->SetEncodingError();
+        stream->SetError();
         return -1;
     }
     const int result = std::ungetc(value, GetNativeStream(stream));
@@ -69,6 +69,11 @@ int APS5_VABI ungetc_nid_postfix(int value, FileStream* stream) {
     return result;
 }
 char* APS5_VABI fgets_nid_postfix(char* buffer, int size, FileStream* stream) {
+    if (size <= 0) {
+        stream->SetError();
+        errno = 22;
+        return nullptr;
+    }
     auto* result = std::fgets(buffer, size, GetNativeStream(stream));
     stream->SyncStatus();
     return result;
diff --git a/core/libs/tests/GuestStandardStreams.cpp b/core/libs/tests/GuestStandardStreams.cpp
index 5de08e2cb..3173ea8d9 100644
--- a/core/libs/tests/GuestStandardStreams.cpp
+++ b/core/libs/tests/GuestStandardStreams.cpp
@@ -8,6 +8,7 @@
 #include <fstream>
 #include <iterator>
 #include <initializer_list>
+#include <limits>
 #include <chrono>
 #include <atomic>
 #include <thread>
@@ -121,7 +122,7 @@ static void CheckUnlockedStreams() {
     Require(std::ungetc('Q', stream.GetHandle()) == 'Q');
     Require(getc_unlocked_nid_postfix(&stream) == 'Q' && !(guest.flags & 0x20));
     std::rewind(stream.GetHandle());
-    stream.SetEncodingError();
+    stream.SetError();
     Require(putc_unlocked_nid_postfix('R', &stream) == 'R' && (guest.flags & 0x40));
     clearerr_nid_postfix(&stream);
     Require(!(guest.flags & 0x40));
@@ -229,6 +230,27 @@ static void CheckUnlockedStreamLock(bool write) {
     stream.Close();
 }
 
+static void CheckFgetsSize() {
+    FileStream stream(std::tmpfile());
+    Require(fwrite_nid_postfix("line\n", 1, 5, &stream) == 5);
+    rewind_nid_postfix(&stream);
+    for (const int size : {0, -1, std::numeric_limits<int>::min()}) {
+        char buffer[8];
+        std::memset(buffer, '!', sizeof(buffer));
+        *__error_nid_postfix() = 0;
+        Require(fgets_nid_postfix(buffer, size, &stream) == nullptr);
+        Require(*__error_nid_postfix() == 22 && ferror_nid_postfix(&stream) != 0 && feof_nid_postfix(&stream) == 0);
+        Require(buffer[0] == '!' && ftello_nid_postfix(&stream) == 0);
+        Require(ferror_nid_postfix(&stream) != 0);
+        clearerr_nid_postfix(&stream);
+        Require(ferror_nid_postfix(&stream) == 0);
+    }
+    char line[8]{};
+    Require(fgets_nid_postfix(line, sizeof(line), &stream) == line && std::strcmp(line, "line\n") == 0);
+    Require(ferror_nid_postfix(&stream) == 0);
+    stream.Close();
+}
+
 static void CheckRewind() {
     FileStream stream(std::tmpfile());
     Require(fwrite_nid_postfix("ab", 1, 2, &stream) == 2);
@@ -239,7 +261,7 @@ static void CheckRewind() {
     rewind_nid_postfix(&stream);
     Require(fgetc_nid_postfix(&stream) == 'a' && fgetc_nid_postfix(&stream) == 'b' && fgetc_nid_postfix(&stream) == EOF);
     Require(feof_nid_postfix(&stream) != 0);
-    stream.SetEncodingError();
+    stream.SetError();
     Require(ferror_nid_postfix(&stream) != 0);
     rewind_nid_postfix(&stream);
     Require(feof_nid_postfix(&stream) == 0 && ferror_nid_postfix(&stream) == 0 && fgetc_nid_postfix(&stream) == 'a');
@@ -511,6 +533,7 @@ int main() {
     Require(fgetc_nid_postfix(&locked) == 'A' && fgetc_nid_postfix(&locked) == 'B');
     locked.Close();
     CheckRewind();
+    CheckFgetsSize();
     CheckUnlockedStreams();
     CheckUnlockedStreamLock(false);
     CheckUnlockedStreamLock(true);