In spoken language comprehension, syntactic parsing decisions interact with prosodic phrasing, which is directly affected by phrase length. Here we used ERPs to examine whether a similar effect holds for the on-line processing of written sentences during silent reading, as suggested by theories of “implicit prosody.” Ambiguous Korean sentence beginnings with two distinct interpretations were manipulated by increasing the length of sentence-initial subject noun phrases (NPs). As expected, only long NPs triggered an additional prosodic boundary reflected by a closure positive shift (CPS) in ERPs. When sentence materials further downstream disambiguated the initially dispreferred interpretation, the resulting P600 component reflecting processing difficulties (“garden path” effects) was smaller in amplitude for sentences with long NPs. Interestingly, additional prosodic revisions required only for the short subject disambiguated condition—the delayed insertion of an implicit prosodic boundary after the subject NP—were reflected by a frontal P600-like positivity, which may be interpreted in terms of a delayed CPS brain response. These data suggest that the subvocally generated prosodic boundary after the long subject NP facilitated the recovery from a garden path, thus primarily supporting one of two competing theoretical frameworks on implicit prosody. Our results underline the prosodic nature of the cognitive processes underlying phrase length effects and contribute cross-linguistic evidence regarding the on-line use of implicit prosody for parsing decisions in silent reading.