diff --git a/Common/Data/Encoding/Utf8.cpp b/Common/Data/Encoding/Utf8.cpp
index 73c48c4819..09abf6090d 100644
--- a/Common/Data/Encoding/Utf8.cpp
+++ b/Common/Data/Encoding/Utf8.cpp
@@ -312,14 +312,19 @@ size_t encode_utf8_modified(uint32_t code_point, unsigned char* output) {
 // A function to convert regular UTF-8 to Java Modified UTF-8. Only used on Android.
 // Written by ChatGPT and corrected and modified.
 void ConvertUTF8ToJavaModifiedUTF8(std::string *output, std::string_view input) {
+	// The overflow can't really happen on 64-bit, but let's do the check anyway.
+	if (input.length() > SIZE_MAX / 6) {
+		output->clear();
+		return;
+	}
 	output->resize(input.length() * 6); // worst case: every input character is encoded as 6 bytes. Can't really plausibly happen, though.
 	size_t out_idx = 0;
 	for (size_t i = 0; i < input.length(); ) {
 		unsigned char c = input[i];
 		if (c == 0) {
 			// Encode null character as 0xC0 0x80. TODO: We probably don't need to support this?
-			output[out_idx++] = (char)0xC0;
-			output[out_idx++] = (char)0x80;
+			(*output)[out_idx++] = (char)0xC0;
+			(*output)[out_idx++] = (char)0x80;
 			i++;
 		} else if ((c & 0xF0) == 0xF0) { // 4-byte sequence (U+10000 to U+10FFFF)
 			if (i + 4 > input.length()) {
diff --git a/Core/HLE/sceKernelModule.cpp b/Core/HLE/sceKernelModule.cpp
index 82f7b989f8..c81607eba7 100644
--- a/Core/HLE/sceKernelModule.cpp
+++ b/Core/HLE/sceKernelModule.cpp
@@ -1096,8 +1096,8 @@ static PSPModule *__KernelLoadELFFromPtr(const u8 *ptr, size_t elfSize, u32 load
 			// In this case it's definitely not compressed. Added assert below.
 		}
 
-		// Don't accept ELFs over 24MB.
-		if (decryptedSize > 24 * 1024 * 1024) {
+		// Don't accept ELFs over 24MB - nor ones with negative size, of course.
+		if (decryptedSize < 0 || decryptedSize > 24 * 1024 * 1024) {
 			*error_string = StringFromFormat("ELF/PRX corrupt, unreasonable decrypted size: %d", (u32)decryptedSize);
 			// TODO: Might be the wrong error code.
 			error = SCE_KERNEL_ERROR_FILEERR;
@@ -1110,7 +1110,7 @@ static PSPModule *__KernelLoadELFFromPtr(const u8 *ptr, size_t elfSize, u32 load
 
 			// Can't decompress in place so we need a temporary buffer.
 			u8 *temp = (u8 *)malloc(decryptedSize);
-			_assert_msg_(temp != nullptr, "Failed to allocate gzip decompression buffer");
+			_assert_msg_(temp != nullptr, "Failed to allocate gzip decompression buffer (decryptedSize: %d)", decryptedSize);
 			memcpy(temp, ptr, decryptedSize);
 			int outBytes = gzipDecompress((u8 *)ptr, maxElfSize, temp);
 			if (outBytes < 0) {