diff --git a/Core/HLE/sceDeflt.cpp b/Core/HLE/sceDeflt.cpp
index b2c29ea2f1..fdf7b0d55c 100644
--- a/Core/HLE/sceDeflt.cpp
+++ b/Core/HLE/sceDeflt.cpp
@@ -38,7 +38,8 @@ static int CommonDecompress(int windowBits, u32 OutBuffer, int OutBufferLength,
 	z_stream stream{};
 	u8 *outBufferPtr = Memory::GetPointer(OutBuffer);
 	stream.next_in = (Bytef*)Memory::GetPointer(InBuffer);
-	stream.avail_in = (uInt)OutBufferLength;
+	// We don't know the available length, just let it use as much as it wants.
+	stream.avail_in = (uInt)Memory::ValidSize(InBuffer, Memory::g_MemorySize);
 	stream.next_out = outBufferPtr;
 	stream.avail_out = (uInt)OutBufferLength;