Where testimony of an in-custody informant is introduced at trial, the court has a sua sponte duty to instruct that the testimony must be corroborated and prejudice resulting from failure to do so is assessed under the Watson standard. Appellant was convicted of the first degree murder of his mother. At trial, appellant’s fellow inmate testified that appellant told him that he killed his mother after enduring years of verbal abuse from her. The court did not instruct the jury that the inmate’s testimony must be corroborated by other evidence that connects defendant with the commission of the offense. Penal Code section 1111.5 (corroboration of in-custody informant) provides that a defendant may not be convicted of an offense based on the uncorroborated testimony of an in-custody informant. Corroboration must be provided by evidence that connects defendant to the offense and not simply evidence that “tends to connect,” as is the standard for accomplice testimony. The court agreed with appellant that failure to instruct the jury as to this requirement is to be measured under the Watson standard; i.e., reversal is required if it is reasonably probable that the jury would have reached a result more favorable to defendant if the trial court instructed as to the corroborating evidence requirement. Here, although the trial court erred in failing to instruct on corroborating evidence, the error was harmless. The mother’s blood was found on clothing in appellant’s bedroom and a statement from appellant’s neighbor provided appellant’s motive for the killing.