diff --git a/racket/src/racket/gc/misc.c b/racket/src/racket/gc/misc.c
index 7b1a37bbaa..692a449941 100644
--- a/racket/src/racket/gc/misc.c
+++ b/racket/src/racket/gc/misc.c
@@ -1196,7 +1196,7 @@ static void get_size(struct hblk *h, word lptr)
 
   *(long *)lptr += bytes;
 }
-long GC_get_memory_use()
+long GC_get_memory_use(void)
 {
   long c = 0;
   LOCK();
diff --git a/racket/src/racket/sgc/sgc.c b/racket/src/racket/sgc/sgc.c
index 5cf6ab8b11..255c05baf2 100644
--- a/racket/src/racket/sgc/sgc.c
+++ b/racket/src/racket/sgc/sgc.c
@@ -2221,17 +2221,17 @@ void GC_dump(void)
   FPRINTF(STDERR, "End Map\n");
 }
 
-size_t GC_get_memory_use()
+size_t GC_get_memory_use(void)
 {
   return (size_t)mem_real_use;
 }
 
-size_t GC_get_memory_peak_use()
+size_t GC_get_memory_peak_use(void)
 {
   return (size_t)mem_peak_use;
 }
 
-size_t GC_get_total_bytes()
+size_t GC_get_total_bytes(void)
 {
   return (size_t)mem_cumulative_use;
 }
@@ -4505,7 +4505,7 @@ void GC_push_all_stack(void *sp, void *ep)
   prepare_stack_collect();
 }
 
-void GC_flush_mark_stack()
+void GC_flush_mark_stack(void)
 {
   collect();  
 }
diff --git a/racket/src/racket/sgc/sgc.h b/racket/src/racket/sgc/sgc.h
index 5130affec6..20ea00d088 100644
--- a/racket/src/racket/sgc/sgc.h
+++ b/racket/src/racket/sgc/sgc.h
@@ -35,9 +35,9 @@ SGC_EXTERN void *GC_base(void *);
 
 SGC_EXTERN void GC_dump(void);
 
-SGC_EXTERN size_t GC_get_memory_use();
-SGC_EXTERN size_t GC_get_memory_peak_use();
-SGC_EXTERN size_t GC_get_total_bytes();
+SGC_EXTERN size_t GC_get_memory_use(void);
+SGC_EXTERN size_t GC_get_memory_peak_use(void);
+SGC_EXTERN size_t GC_get_total_bytes(void);
 
 SGC_EXTERN void GC_end_stubborn_change(void *);
 
@@ -104,9 +104,9 @@ SGC_EXTERN void GC_trace_path(void);
 
 SGC_EXTERN void GC_store_path(void *v, uintptr_t src, void *path_data);
 SGC_EXTERN void **GC_get_next_path(void **prev, int *len);
-SGC_EXTERN void GC_clear_paths();
+SGC_EXTERN void GC_clear_paths(void);
 
-SGC_EXTERN void GC_flush_mark_stack();
+SGC_EXTERN void GC_flush_mark_stack(void);
 SGC_EXTERN void GC_push_all_stack(void *sp, void *ep);
 SGC_EXTERN void GC_register_indirect_disappearing_link(void **p, void *a);