本文探討O'Conner（1976）原始客語聲母系統中兩個舌面鼻音：*n1-與*n2-的擬測問題。O'Conner的方案是將*n1-擬為*ŋ-，*n2-擬為*n-，主要依據是沙頭角客語的讀音。若把O'Conner的擬測與Norman（2011）所提出的漢語方言通音（Common Dialectal Chinese）進行比較，將面臨音韻對應上相當重大的困難。在重新檢視沙頭角客語的音韻系統之後，本文將原始客語的*n1-擬測為*n-，*n2-擬測為*ŋ-。本文提出的方案不僅對內能解釋原始客語的演變，對外也能與漢語方言通音合理地接軌。另外，本文在方法論上有兩個重要的意義：一是依照歷史語言學經典的比較方法，從現代方言的觀點由下而上的建構原始客語，而非直接使用《切韻》來推導演變；二是利用「漢語方言通音」（簡化的《切韻》音系）與原始客語進行比較，從顛倒重建的觀點檢驗不同方案，從而找出更為合理的音值擬測。本文作為個案研究，不僅從方法上展示原始漢語方言擬測的可行性，更期盼喚起學界對原始客語擬測的重視。

In this paper, I reexamine O'Conner's reconstruction (O'Conner 1976) of * n1 and *n2 in his Proto Hakka initial system and address a new proposal for these two phonemes. O'Conner assigned *ŋ to*n1 and *n to *n2 based on the Sā Tóu Jiǎo Hakka dialect. However, when comparing *n1 and *n2 cognates of O'Conner's system with Norman's Common Dialectal Chinese system, we encounter a severe difficulty in phonetic correspondences. After careful investigation of the Sā Tóu Jiǎo Hakka dialect's phonological system, I propose an opposite reconstruction by assigning *ŋ to*n2 and *n to *n1. This approach? could not only explain sound changes in Hakka dialects but also build an efficacious and simple connection with the Common Dialectal Chinese system. Through this case study, I hope to demonstrate methodologically the feasibility of reconstruction in Proto Chinese dialects and evoke the value of reconstruction of Proto Hakka in academia.