A close-talk detector detects a near-end user's speech signal, while an adaptive ANC process is running, and in response helps prevent the filter coefficients of an adaptive filter of the ANC process from being corrupted, thereby reducing the risk of the adaptive filters diverge. Upon detecting speech using a vibration sensor signal and one or more microphone signals, the detector asserts a signal that slows down, or even freezes or halts, the adaptation of the adaptive filter. The signal may be de-asserted when no more speech is being detected, thereby allowing the adaptive ANC process to resume its normal rate adaptation of the filter. The detector may continuously operate in this manner during the call, as the user talks and then pauses and then resumes talking. Other embodiments are also described.