diff --git a/src/GCodes/GCodeInput.cpp b/src/GCodes/GCodeInput.cpp
index 26a5f7a2ad..8416912d56 100644
--- a/src/GCodes/GCodeInput.cpp
+++ b/src/GCodes/GCodeInput.cpp
@@ -126,7 +126,7 @@ bool BufferedStreamGCodeInput::FillBuffer(GCodeBuffer *gb) noexcept
 	const size_t spaceLeft = BufferSpaceLeft();
 	if (spaceLeft >= GCodeInputUSBReadThreshold)
 	{
-		const size_t maxToTransfer = (readingPointer > writingPointer) ? spaceLeft : GCodeInputBufferSize - writingPointer;
+		const size_t maxToTransfer = (readingPointer > writingPointer || writingPointer == 0) ? spaceLeft : GCodeInputBufferSize - writingPointer;
 		writingPointer = (writingPointer + device.readBytes(buffer + writingPointer, maxToTransfer)) % GCodeInputBufferSize;
 	}
 	return StandardGCodeInput::FillBuffer(gb);