diff --git a/core/libs/prx/libc/include/SonyCrt.hpp b/core/libs/prx/libc/include/SonyCrt.hpp
index 2016da156..56fe7b6a1 100644
--- a/core/libs/prx/libc/include/SonyCrt.hpp
+++ b/core/libs/prx/libc/include/SonyCrt.hpp
@@ -125,10 +125,11 @@ inline int SonyWcscpyS(std::uint16_t* dest, std::size_t size, const std::uint16_
 
 inline std::size_t SonyMbstowcs(std::uint16_t* dest, const char* src, std::size_t size) {
     if (!src) return 0;
+    if (!dest) return std::strlen(src);
     std::size_t converted = 0;
     while (converted < size) {
         const auto value = static_cast<unsigned char>(src[converted]);
-        if (dest) dest[converted] = value;
+        dest[converted] = value;
         if (value == 0) return converted;
         ++converted;
     }
diff --git a/core/libs/tests/GuestCrt.cpp b/core/libs/tests/GuestCrt.cpp
index 611ddc32a..f37cb68bb 100644
--- a/core/libs/tests/GuestCrt.cpp
+++ b/core/libs/tests/GuestCrt.cpp
@@ -144,6 +144,8 @@ int main() {
     Require(sceAmprMbstowcs(wide, "ABC", 8) == 3);
     Require(wide[0] == 65 && wide[1] == 66 && wide[2] == 67 && wide[3] == 0);
     Require(sceAmprMbstowcs(nullptr, "ABC", 8) == 3);
+    Require(sceAmprMbstowcs(nullptr, "ABC", 0) == 3 && sceAmprMbstowcs(nullptr, "ABC", 1) == 3);
+    Require(mbstowcs_nid_postfix(nullptr, "ABC", 0) == 3 && mbstowcs_nid_postfix(nullptr, "ABC", 1) == 3);
     Require(sceAmprMbstowcs(wide, "ABC", 2) == 2);
     Require(mbstowcs_nid_postfix(wide, "ABC", 8) == 3);