In this paper I show that the columnar accent of the o-stems can be integrated into a simple accent grammar of PIE. After establishing the general pattern I demonstrate how the accented and unaccented thematic suffixes fit into the picture. The grammatical sketch leads to the conclusion that it is unnecessary to assume any break between a more ancient PIE stratum with consonant stems and a more recent one with vocalic stems, each with its own accent and ablaut patterns. In the second part a morphological network for deriving the accent patterns of internal derivation in o-stems is developed. In a short outlook I show that the simple mechanism of accent inversion developed here also accounts for internal derivation in consonant stems and for accent shifts in compounds.