The role of metalinguistic knowledge in L2/FL learning continues to be a subject of debate. Some researchers downplay its role (Alderson et al, 1997; Elder et al, 1999), but others hypothesise that this knowledge forms a stepping stone towards L2 proficiency (Sorace, 1985; Roehr & Ganem-Gutierrez, 2009). While there is a consensus that writing and reading lend themselves most to its influence, research on its role in speaking is still relatively thin on the ground. Empirical studies indicate that metalinguistic knowledge has a significant effect on child L2 learners' oral linguistic performance (e.g. White and Ranta, 2002; Serrano, 2011). As for adult L2 learners, existing findings show that learners' accurate use of grammar constructions correlates with their ability to articulate explicit rules describing these constructions (e.g. Scheffler and Cinciala, 2010). The current study aimed to explore the potential role of metalinguistic knowledge in oral grammatical accuracy, fluency and self-correction in L1 Arabic university-level learners of English (N = 64), targeting a broad range of grammar constructions. The participants were asked to take a one-to-one speaking test, an English placement test, and a metalinguistic assessment test. In addition, 19 participants took part in stimulated recall of part of their recorded interviews. The results show that there is a positive relationship of moderate strength between metalinguistic knowledge and speaking accuracy, and this relationship appears to be influenced by metalinguistic-related variables, such as perceived difficulty of grammar points and prototypicality of rules. Metalinguistic knowledge also · correlates positively at moderate strength with speaking fluency, represented by words per minute, and negatively at moderate strength with speaking dysfluency, represented by pauses per hundred words. Additionally, metalinguistic knowledge correlates moderately with successful self-correction in speaking. A comparison between learners at different stages of L2 learning gives a piece of evidence for durability of metalinguistic knowledge in a poorly-communicative L2 learning context. The results are most compatible with the explicit-implicit strong interface position.