G. Huet and J. J. Levy (INRIA Rep. 359, 1979) showed that for every strongly sequential orthogonal (i.e., left-linear and non-overlapping) term rewriting system, index reduction strategy is normalizing. Their result is extended to overlapping term rewriting systems. It is shown that index reduction is normalizing for the class of strongly sequential left-linear term rewriting systems in which every critical pair can be joined with root balanced reductions. This class includes all weakly orthogonal left-normal systems, for which a leftmost-outermost reduction strategy is normalizing.