The present study investigates the influence of grammatical and phonological errors on the perceived degree of foreign accent strength. German and Polish participants listened to speech in their native language produced with foreign and native accent. They rated the accent strength of each sentence on a 7-point scale. Grammatical errors consisted of gender agreement violations and phonological errors consisted of controlled vowel substitutions. Both error types significantly affected the perception of accent strength in the foreign and native-accented condition. In Polish, phonological anomalies had significantly more impact than grammatical violations in native-accented sentences. In German, there was no significant difference between phonological and grammatical violations. The study provides evidence that the presence of phonological and grammatical errors increases the perceived accentedness of speech. The weighting of both errors for accent perception can vary between languages.