diff --git a/commit-slab.h b/commit-slab.h
index d4c8286470c1adef499ca30e9f57c7fe4b2be2da..cc114b53b096c6fc8574629b86659a639fdfed61 100644
--- a/commit-slab.h
+++ b/commit-slab.h
@@ -22,8 +22,17 @@
  *
  *   Initializes the indegree slab that associates an array of integers
  *   to each commit. 'stride' specifies how big each array is.  The slab
- *   that id initialied by the variant without "_with_stride" associates
+ *   that is initialized by the variant without "_with_stride" associates
  *   each commit with an array of one integer.
+ *
+ * - void clear_indegree(struct indegree *);
+ *
+ *   Empties the slab.  The slab can be reused with the same stride
+ *   without calling init_indegree() again or can be reconfigured to a
+ *   different stride by calling init_indegree_with_stride().
+ *
+ *   Call this function before the slab falls out of scope to avoid
+ *   leaking memory.
  */
 
 /* allocate ~512kB at once, allowing for malloc overhead */
@@ -31,6 +40,8 @@
 #define COMMIT_SLAB_SIZE (512*1024-32)
 #endif
 
+#define MAYBE_UNUSED __attribute__((__unused__))
+
 #define define_commit_slab(slabname, elemtype) 				\
 									\
 struct slabname {							\
@@ -41,8 +52,8 @@ struct slabname {							\
 };									\
 static int stat_ ##slabname## realloc;					\
 									\
-static void init_ ##slabname## _with_stride(struct slabname *s,		\
-					    unsigned stride)		\
+static MAYBE_UNUSED void init_ ##slabname## _with_stride(struct slabname *s, \
+						   unsigned stride)	\
 {									\
 	unsigned int elem_size;						\
 	if (!stride)							\
@@ -54,12 +65,12 @@ static void init_ ##slabname## _with_stride(struct slabname *s,		\
 	s->slab = NULL;							\
 }									\
 									\
-static void init_ ##slabname(struct slabname *s)			\
+static MAYBE_UNUSED void init_ ##slabname(struct slabname *s)		\
 {									\
 	init_ ##slabname## _with_stride(s, 1);				\
 }									\
 									\
-static void clear_ ##slabname(struct slabname *s)			\
+static MAYBE_UNUSED void clear_ ##slabname(struct slabname *s)		\
 {									\
 	int i;								\
 	for (i = 0; i < s->slab_count; i++)				\
@@ -69,8 +80,8 @@ static void clear_ ##slabname(struct slabname *s)			\
 	s->slab = NULL;							\
 }									\
 									\
-static elemtype *slabname## _at(struct slabname *s,			\
-				const struct commit *c)			\
+static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s,	\
+				       const struct commit *c)		\
 {									\
 	int nth_slab, nth_slot;						\
 									\
@@ -80,7 +91,7 @@ static 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;				\
@@ -94,4 +105,16 @@ static elemtype *slabname## _at(struct slabname *s,			\
 									\
 static int stat_ ##slabname## realloc
 
+/*
+ * Note that this seemingly redundant second declaration is required
+ * to allow a terminating semicolon, which makes instantiations look
+ * like function declarations.  I.e., the expansion of
+ *
+ *    define_commit_slab(indegree, int);
+ *
+ * ends in 'static int stat_indegreerealloc;'.  This would otherwise
+ * be a syntax error according (at least) to ISO C.  It's hard to
+ * catch because GCC silently parses it by default.
+ */
+
 #endif /* COMMIT_SLAB_H */