diff --git a/commit-slab.h b/commit-slab.h
index d068e2d531..cc114b53b0 100644
--- a/commit-slab.h
+++ b/commit-slab.h
@@ -91,7 +91,7 @@ static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s,	\
 	if (s->slab_count <= nth_slab) {				\
 		int i;							\
 		s->slab = xrealloc(s->slab,				\
-				   (nth_slab + 1) * sizeof(s->slab));	\
+				   (nth_slab + 1) * sizeof(*s->slab));	\
 		stat_ ##slabname## realloc++;				\
 		for (i = s->slab_count; i <= nth_slab; i++)		\
 			s->slab[i] = NULL;				\