diff --git a/core/libs/prx/libSceConvertKeycode/ImeKeyboardType.hpp b/core/libs/prx/libSceConvertKeycode/ImeKeyboardType.hpp
index 4ace3c252c..ec7e041937 100644
--- a/core/libs/prx/libSceConvertKeycode/ImeKeyboardType.hpp
+++ b/core/libs/prx/libSceConvertKeycode/ImeKeyboardType.hpp
@@ -35,7 +35,7 @@ constexpr std::uint32_t LookUp(std::int32_t keyboardType, std::int32_t japaneseV
         constexpr std::uint32_t traditionalChinese[] = {26, 27, 28, 29, 39};
         return traditionalChineseVariant >= 0 && traditionalChineseVariant < 5 ? traditionalChinese[traditionalChineseVariant] : 0;
     }
-    const std::int32_t index = keyboardType - kFirstMappedType;
+    const std::int64_t index = std::int64_t{keyboardType} - kFirstMappedType;
     return index >= 0 && index < kMappedTypeCount ? kImeTypeByKeyboardType[index] : 0;
 }
 
diff --git a/core/libs/tests/GuestConvertKeycode.cpp b/core/libs/tests/GuestConvertKeycode.cpp
index 8bf7b815b0..d2d3cb463f 100644
--- a/core/libs/tests/GuestConvertKeycode.cpp
+++ b/core/libs/tests/GuestConvertKeycode.cpp
@@ -15,6 +15,9 @@
 
 static void Require(bool value) { if (!value) std::abort(); }
 
+static_assert(ImeKeyboardType::LookUp(INT32_MIN, 0, 0) == 0);
+static_assert(ImeKeyboardType::LookUp(INT32_MAX, 0, 0) == 0);
+
 static void SetLanguage(const char* value) {
 #ifdef _WIN32
     Require(_putenv_s("ANYPS5_LANGUAGE", value != nullptr ? value : "") == 0);