This paper explores the number marking challenges faced by L2 learners of English whose L1 is one of the classifier languages Mandarin Chinese (henceforth Chinese) or Bahasa Indonesia (henceforth Indonesian). It examines whether these groups differ in their marking of English number, and how the speaker's level of proficiency, as well as linguistic factors including countability, concreteness, and determiner use, interact and influence their performance. The present study differs from previous studies in that it offers unique insights from authentic spoken data. The authors extracted 4000 tokens from the Chinese and Indonesian spoken monolog components in the International Corpus Network of Asian Learners of English (ICNALE), involving 150 Chinese-speaking and 100 Indonesian-speaking learners across beginner and intermediate proficiency; the tokens were part-of-speech tagged and annotated. Although the analysis, using mixed-effects binomial logistic regression, revealed no performance differences between the groups and no significant proficiency effects, the study found a strong relationship between ungrammatical number marking and count nouns, particularly abstract count nouns (e.g., "taking part-time job"), as well as the absence of determiners (e.g., "smoking in restaurant"). These findings confirm that learners from classifier languages face significant challenges with count nouns and that inaccurate number marking often occurs where nouns appear unmarked for number in their L1. The paper concludes with pedagogical suggestions.