diff --git a/alloc.c b/alloc.c
index c2fc5d6888..e7aa81b7aa 100644
--- a/alloc.c
+++ b/alloc.c
@@ -36,7 +36,7 @@ struct alloc_state {
 	int slab_nr, slab_alloc;
 };
 
-void *allocate_alloc_state(void)
+struct alloc_state *allocate_alloc_state(void)
 {
 	return xcalloc(1, sizeof(struct alloc_state));
 }
diff --git a/alloc.h b/alloc.h
index 7a41bb9eb3..ba356ed847 100644
--- a/alloc.h
+++ b/alloc.h
@@ -15,7 +15,7 @@ void *alloc_object_node(struct repository *r);
 void alloc_report(struct repository *r);
 unsigned int alloc_commit_index(struct repository *r);
 
-void *allocate_alloc_state(void);
+struct alloc_state *allocate_alloc_state(void);
 void clear_alloc_state(struct alloc_state *s);
 
 #endif