diff --git a/celt/celt_encoder.c b/celt/celt_encoder.c
index ad0ebf0ac3bd39b474227698f5dba319b4ac1f6b..66b5f00dfd55480ccb4cd3cb0d9bfc0f71d495a4 100644
--- a/celt/celt_encoder.c
+++ b/celt/celt_encoder.c
@@ -1724,7 +1724,7 @@ int celt_encode_with_ec(CELTEncoder * OPUS_RESTRICT st, const opus_val16 * pcm,
    compute_mdcts(mode, shortBlocks, in, freq, C, CC, LM, st->upsample, st->arch);
    /* This should catch any NaN in the CELT input. Since we're not supposed to see any (they're filtered
       at the Opus layer), just abort. */
-   celt_assert(!celt_isnan(freq[0]) && (C==1 || !celt_isnan(freq[C*N])));
+   celt_assert(!celt_isnan(freq[0]) && (C==1 || !celt_isnan(freq[N])));
    if (CC==2&&C==1)
       tf_chan = 0;
    compute_band_energies(mode, freq, bandE, effEnd, C, LM, st->arch);