diff --git a/src/backend.cmod b/src/backend.cmod
index 860738f90b11e08164ae08c39209a63fc5be77f3..0dd22dbee8c6962393aa218034806d055b8b63bc 100644
--- a/src/backend.cmod
+++ b/src/backend.cmod
@@ -138,7 +138,7 @@ struct program * PollDeviceBackend_program;
 
 /* Declarations for the legacy backend interface stuff. */
 
-static struct compat_cb_box * alloc_compat_cb_box();
+static struct compat_cb_box * alloc_compat_cb_box(void);
 static void really_free_compat_cb_box(struct compat_cb_box * b);
 static int compat_box_dispatcher (struct fd_callback_box *box, int event);
 
@@ -208,7 +208,7 @@ static int backend_do_call_outs(struct Backend_struct *me);
 static void backend_verify_call_outs(struct Backend_struct *me);
 #endif
 #ifdef DO_PIKE_CLEANUP
-static void backend_cleanup();
+static void backend_cleanup(void);
 #endif
 
 struct Backend_struct *get_backend_for_fd(int fd)
@@ -5664,7 +5664,7 @@ struct compat_cb_box
 
 static struct block_allocator compat_cb_allocator = BA_INIT_PAGES(sizeof(struct compat_cb_box), 1);
 
-static struct compat_cb_box * alloc_compat_cb_box() {
+static struct compat_cb_box * alloc_compat_cb_box(void) {
     return ba_alloc(&compat_cb_allocator);
 }
 
@@ -5676,7 +5676,7 @@ void count_memory_in_compat_cb_boxs(size_t * n, size_t * s) {
     ba_count_all(&compat_cb_allocator, n, s);
 }
 
-void free_all_compat_cb_box_blocks() {
+void free_all_compat_cb_box_blocks(void) {
     ba_destroy(&compat_cb_allocator);
 }
 
@@ -6001,7 +6001,7 @@ void exit_backend(void)
 
 /* Note: This is called when the last backend object exits, which might be
  * after exit_backend if there's garbage. */
-static void backend_cleanup()
+static void backend_cleanup(void)
 {
 #ifdef OPEN_POLL_DEVICE
   if (pdb_backends) {
diff --git a/src/backend.h b/src/backend.h
index 54f2c4911063d1024cc032ef81c121d8b61a4a9a..3e84c888b9379235d5a98bdbd92c2651b734d3b0 100644
--- a/src/backend.h
+++ b/src/backend.h
@@ -81,7 +81,7 @@ extern struct callback_list do_debug_callbacks;
 PMOD_EXPORT extern struct program *Backend_program;
 
 void count_memory_in_compat_cb_boxs(size_t *num, size_t *size);
-void free_all_compat_cb_box_blocks();
+void free_all_compat_cb_box_blocks(void);
 
 PMOD_EXPORT void debug_check_fd_not_in_use (int fd);
 #if 1
diff --git a/src/builtin.cmod b/src/builtin.cmod
index fa753b545bea8b179249c8986c3acbc5fad1516e..c0bcc40b26543d9a2504424c1e7391f51729c1e7 100644
--- a/src/builtin.cmod
+++ b/src/builtin.cmod
@@ -5044,7 +5044,7 @@ void count_memory_in_pike_list_nodes(size_t * n, size_t * s) {
     ba_count_all(&pike_list_node_allocator, n, s);
 }
 
-void free_all_pike_list_node_blocks() {
+void free_all_pike_list_node_blocks(void) {
     ba_destroy(&pike_list_node_allocator);
 }
 
@@ -6064,7 +6064,7 @@ PIKECLASS MasterCodec
 
 static struct object *val_module;
 
-static void get_val_module()
+static void get_val_module(void)
 {
   assert (!val_module);
   push_text ("Val");
diff --git a/src/builtin_functions.h b/src/builtin_functions.h
index 2c889573562026961cb3e25d1b2aed39d8ed1642..e8a84aff9c3e8695887c7f90bdf62d19da0d4d86 100644
--- a/src/builtin_functions.h
+++ b/src/builtin_functions.h
@@ -209,7 +209,7 @@ struct pike_list_node
   struct svalue val;
 };
 void count_memory_in_pike_list_nodes(size_t * n, size_t * s);
-void free_all_pike_list_node_blocks();
+void free_all_pike_list_node_blocks(void);
 PMOD_EXPORT void free_list_node(struct pike_list_node *node);
 PMOD_EXPORT void unlink_list_node(struct pike_list_node *n);
 PMOD_EXPORT void prepend_list_node(struct pike_list_node *node,
diff --git a/src/constants.c b/src/constants.c
index 7cf807dff13fce36666fc708d1d6ab0ac2efcab2..d09ed922df74acb1701b4b9a081c00e8f1c6375f 100644
--- a/src/constants.c
+++ b/src/constants.c
@@ -85,7 +85,7 @@ void really_free_callable(struct callable * c) {
 void count_memory_in_callables(size_t * num, size_t * size) {
     ba_count_all(&callable_allocator, num, size);
 }
-void free_all_callable_blocks() {
+void free_all_callable_blocks(void) {
     ba_destroy(&callable_allocator);
 }
 
diff --git a/src/constants.h b/src/constants.h
index 4357e2035e3504be98b50ec9bd0bc3cacff5c581..8ed227eab3b1fab674d3c78a1ae6e592c0e30789 100644
--- a/src/constants.h
+++ b/src/constants.h
@@ -49,7 +49,7 @@ void add_pike_string_constant(const char *name, const char *str, int len);
 PMOD_EXPORT void add_global_program(const char *name, struct program *p);
 void really_free_callable(struct callable * c);
 void count_memory_in_callables(size_t * num, size_t * size);
-void free_all_callable_blocks();
+void free_all_callable_blocks(void);
 PMOD_EXPORT struct callable *low_make_callable(c_fun fun,
 				   struct pike_string *name,
 				   struct pike_type *type,
diff --git a/src/fdlib.c b/src/fdlib.c
index b189c643689189494653236e6029102c9ed1195e..f56fe004ac83b13af768efabbd1102a18e1df066 100644
--- a/src/fdlib.c
+++ b/src/fdlib.c
@@ -152,7 +152,7 @@ PMOD_EXPORT int debug_fd_query_properties(int fd, int guess)
   }
 }
 
-void fd_init()
+void fd_init(void)
 {
   int e;
   WSADATA wsadata;
@@ -179,7 +179,7 @@ void fd_init()
   mt_unlock(&fd_mutex);
 }
 
-void fd_exit()
+void fd_exit(void)
 {
   WSACleanup();
   mt_destroy(&fd_mutex);
diff --git a/src/fdlib.h b/src/fdlib.h
index c44ad39f73e149d0b52f787ab920643a070e753d..07f4275434ce71a5cf16a2d2e18fb21e9350b517 100644
--- a/src/fdlib.h
+++ b/src/fdlib.h
@@ -121,8 +121,8 @@ typedef off_t PIKE_OFF_T;
 PMOD_EXPORT void set_errno_from_win32_error (unsigned long err);
 PMOD_EXPORT char *debug_fd_info(int fd);
 PMOD_EXPORT int debug_fd_query_properties(int fd, int guess);
-void fd_init();
-void fd_exit();
+void fd_init(void);
+void fd_exit(void);
 PMOD_EXPORT int debug_fd_stat(const char *file, PIKE_STAT_T *buf);
 PMOD_EXPORT FD debug_fd_open(const char *file, int open_mode, int create_mode);
 PMOD_EXPORT FD debug_fd_socket(int domain, int type, int proto);
diff --git a/src/gc.c b/src/gc.c
index 711723265feaa56414c0abb77f7f645f3693b7f7..e8ef840e057b1eb393b9d42a52fcfc9634538370 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -1760,7 +1760,7 @@ struct gc_queue_block *gc_mark_first = NULL, *gc_mark_last = NULL;
 
 #define CHECK_MARK_QUEUE_EMPTY() assert (!gc_mark_first)
 
-void gc_mark_run_queue()
+void gc_mark_run_queue(void)
 {
   struct gc_queue_block *b;
 
@@ -1779,7 +1779,7 @@ void gc_mark_run_queue()
   gc_mark_last=0;
 }
 
-void gc_mark_discard_queue()
+void gc_mark_discard_queue(void)
 {
   struct gc_queue_block *b = gc_mark_first;
   while (b)
diff --git a/src/gc.h b/src/gc.h
index f64283f0f59ea0116f245e3816c28b7eb1b15d8f..ce88582d9ae25e4e14451482f2f531b86d1bd11e 100644
--- a/src/gc.h
+++ b/src/gc.h
@@ -388,8 +388,8 @@ void cleanup_gc(void);
 #ifdef GC_MARK_DEBUG
 
 void gc_mark_enqueue (queue_call fn, void *data);
-void gc_mark_run_queue();
-void gc_mark_discard_queue();
+void gc_mark_run_queue(void);
+void gc_mark_discard_queue(void);
 
 #else  /* !GC_MARK_DEBUG */
 
diff --git a/src/interpret.c b/src/interpret.c
index ffd6458f06db246824b4780ecb6a0e2e341caf8b..14f3f57a51b51286ec098d2b6aff954079afc4fc 100644
--- a/src/interpret.c
+++ b/src/interpret.c
@@ -1370,7 +1370,7 @@ void *dummy_label = NULL;
 /* Intended to be called from machine code before inlined function
  * calls (primarily the CALL_BUILTIN opcodes), to ensure thread
  * switching. */
-void call_check_threads_etc()
+void call_check_threads_etc(void)
 {
   FAST_CHECK_THREADS_ON_CALL();
 }
@@ -1379,7 +1379,7 @@ void call_check_threads_etc()
     defined(INS_F_JUMP_WITH_ARG) || defined(INS_F_JUMP_WITH_TWO_ARGS)
 /* Intended to be called from machine code on backward branch jumps,
  * to ensure thread switching. */
-void branch_check_threads_etc()
+void branch_check_threads_etc(void)
 {
   FAST_CHECK_THREADS_ON_BRANCH();
 }
diff --git a/src/interpret.h b/src/interpret.h
index cd16d0d0e4c1b7426b4291211f27bdf4294669ed..3ae953c8c39eb559c170bfaa240acc350c0e7eba 100644
--- a/src/interpret.h
+++ b/src/interpret.h
@@ -755,10 +755,10 @@ void count_memory_in_pike_frames(size_t*, size_t*);
 /*BLOCK_ALLOC(pike_frame,128);*/
 
 #ifdef PIKE_USE_MACHINE_CODE
-void call_check_threads_etc();
+void call_check_threads_etc(void);
 #if defined(OPCODE_INLINE_BRANCH) || defined(INS_F_JUMP) || \
     defined(INS_F_JUMP_WITH_ARG) || defined(INS_F_JUMP_WITH_TWO_ARGS)
-void branch_check_threads_etc();
+void branch_check_threads_etc(void);
 #endif
 #ifdef OPCODE_INLINE_RETURN
 PIKE_OPCODE_T *inter_return_opcode_F_CATCH(PIKE_OPCODE_T *addr);
diff --git a/src/mapping.c b/src/mapping.c
index 534a148aebcec57a73a935d7169e5b989e875632..ab52f4d18303a1ed5a3bd480d61c8054c9506728 100644
--- a/src/mapping.c
+++ b/src/mapping.c
@@ -70,11 +70,11 @@ void really_free_mapping(struct mapping * m) {
 }
 
 ATTRIBUTE((malloc))
-static struct mapping * alloc_mapping() {
+static struct mapping * alloc_mapping(void) {
     return ba_alloc(&mapping_allocator);
 }
 
-void free_all_mapping_blocks() {
+void free_all_mapping_blocks(void) {
     ba_destroy(&mapping_allocator);
 }
 
diff --git a/src/mapping.h b/src/mapping.h
index abec6e3f95c3d7b3314a4848670becf30757da14..f4e11165c5358b51b3dc12d9bac75b4ba66e9116 100644
--- a/src/mapping.h
+++ b/src/mapping.h
@@ -388,7 +388,7 @@ void simple_describe_mapping(struct mapping *m);
 void debug_dump_mapping(struct mapping *m);
 int mapping_is_constant(struct mapping *m,
 			struct processing *p);
-void free_all_mapping_blocks();
+void free_all_mapping_blocks(void);
 
 /* Prototypes end here */
 
diff --git a/src/object.c b/src/object.c
index e2ad36beec1f4db670cbcb6aad42c9a30f4648d8..dc21d93ccc35efd41db3bf27b68dab9d2e710b2b 100644
--- a/src/object.c
+++ b/src/object.c
@@ -106,11 +106,11 @@ void really_free_object(struct object * o) {
 }
 
 ATTRIBUTE((malloc))
-struct object * alloc_object() {
+struct object * alloc_object(void) {
     return ba_alloc(&object_allocator);
 }
 
-void free_all_object_blocks() {
+void free_all_object_blocks(void) {
     ba_destroy(&object_allocator);
 }
 
diff --git a/src/object.h b/src/object.h
index e2f22f629aae80c83aceb81fa09b690b09ca2a0d..4e3f6d91d2fb795d90bcba3db6791f0d8918bd6e 100644
--- a/src/object.h
+++ b/src/object.h
@@ -82,7 +82,7 @@ enum object_destruct_reason {
 ATTRIBUTE((malloc)) struct object * alloc_object();
 void really_free_object(struct object * o);
 void count_memory_in_objects(size_t *_num, size_t *_size);
-void free_all_object_blocks();
+void free_all_object_blocks(void);
 PMOD_EXPORT struct object *low_clone(struct program *p);
 PMOD_EXPORT void call_c_initializers(struct object *o);
 PMOD_EXPORT void call_prog_event(struct object *o, int event);
diff --git a/src/pike_types.c b/src/pike_types.c
index 12dec6edd4cdf8daa4af0f1d00b5be6876d764c0..9b2d2bcb82ed657de18a48bd75991a4f8b3b074d 100644
--- a/src/pike_types.c
+++ b/src/pike_types.c
@@ -301,7 +301,7 @@ PMOD_EXPORT void really_free_pike_type(struct pike_type * t) {
 }
 
 ATTRIBUTE((malloc))
-PMOD_EXPORT struct pike_type * alloc_pike_type() {
+PMOD_EXPORT struct pike_type * alloc_pike_type(void) {
     return ba_alloc(&type_allocator);
 }
 
@@ -8469,7 +8469,7 @@ static void low_make_pike_type(unsigned char *type_string,
   }
 }
 
-void type_stack_mark()
+void type_stack_mark(void)
 {
   if(UNLIKELY(Pike_compiler->pike_type_mark_stackp >= pike_type_mark_stack + (PIKE_TYPE_STACK_SIZE>>4)))
     Pike_fatal("Type mark stack overflow.\n");
diff --git a/src/pike_types.h b/src/pike_types.h
index 166bec42a572ba5a0e898caa6f11fd287f25992d..8991d7bd73154be95310de6b13b09a06c0792cb8 100644
--- a/src/pike_types.h
+++ b/src/pike_types.h
@@ -206,7 +206,7 @@ void debug_push_reverse_type(unsigned int type);
 #define push_reverse_type debug_push_reverse_type
 #endif /* DEBUG_MALLOC */
 
-extern void type_stack_mark();
+extern void type_stack_mark(void);
 
 #define reset_type_stack() do {			\
    type_stack_pop_to_mark();			\
@@ -215,7 +215,7 @@ extern void type_stack_mark();
 
 /* Prototypes begin here */
 PMOD_EXPORT void really_free_pike_type(struct pike_type * t);
-PMOD_EXPORT ATTRIBUTE((malloc)) struct pike_type * alloc_pike_type();
+PMOD_EXPORT ATTRIBUTE((malloc)) struct pike_type * alloc_pike_type(void);
 PMOD_EXPORT void count_memory_in_pike_types(size_t *n, size_t *s);
 void debug_check_type_string(struct pike_type *s);
 void init_types(void);
diff --git a/src/program.c b/src/program.c
index 7d0348f8521a676d3aa13848d53a5afb9956f875..416e7ed49407f84a160fe544940431ce7c720698 100644
--- a/src/program.c
+++ b/src/program.c
@@ -93,7 +93,7 @@ static size_t add_xstorage(size_t size,
 static struct block_allocator program_allocator = BA_INIT_PAGES(sizeof(struct program), 4);
 
 ATTRIBUTE((malloc))
-struct program * alloc_program() {
+struct program * alloc_program(void) {
     return ba_alloc(&program_allocator);
 }
 
@@ -112,7 +112,7 @@ void count_memory_in_programs(size_t *num, size_t *_size) {
     *_size = size;
 }
 
-void free_all_program_blocks() {
+void free_all_program_blocks(void) {
     ba_destroy(&program_allocator);
 }
 
diff --git a/src/program.h b/src/program.h
index bd3428faaa173c70b2323a3cf0d26e85f7aa52e1..65cba84b4afd75a5d589e94e49d4b4bdcdd0ca65 100644
--- a/src/program.h
+++ b/src/program.h
@@ -695,10 +695,10 @@ PMOD_EXPORT void gc_check_zapped (void *a, TYPE_T type, const char *file, INT_TY
 #endif
 
 ATTRIBUTE((malloc))
-PMOD_EXPORT struct program * alloc_program();
+PMOD_EXPORT struct program * alloc_program(void);
 PMOD_EXPORT void really_free_program(struct program * p);
 void count_memory_in_programs(size_t *num, size_t *_size);
-void free_all_program_blocks();
+void free_all_program_blocks(void);
 
 
 extern struct program *first_program;
diff --git a/src/rbtree.c b/src/rbtree.c
index e76a19b71be8db39781ce1b93b1b8bdceb16d524..dba33065971bb311b63fa9a877cbe40ff1705495 100644
--- a/src/rbtree.c
+++ b/src/rbtree.c
@@ -1619,7 +1619,7 @@ size_t rbstack_slice_allocs = 0;
 size_t rb_num_adds = 0, rb_add_rebalance_cnt = 0;
 size_t rb_num_deletes = 0, rb_del_rebalance_cnt = 0;
 
-void reset_rb_stats()
+void reset_rb_stats(void)
 {
   rb_num_sidesteps = rb_num_sidestep_ops = 0;
   rb_num_finds = rb_find_depth = 0;
diff --git a/src/rbtree.h b/src/rbtree.h
index eac23b82316e8313bc89b95d02130919cec9e1fe..c5a40132f00bd2708f538b4123e8742aad5c88ef 100644
--- a/src/rbtree.h
+++ b/src/rbtree.h
@@ -225,7 +225,7 @@ extern size_t rb_num_traverses, rb_num_traverse_ops;
 extern size_t rbstack_slice_allocs;
 extern size_t rb_num_adds, rb_add_rebalance_cnt;
 extern size_t rb_num_deletes, rb_del_rebalance_cnt;
-void reset_rb_stats();
+void reset_rb_stats(void);
 void print_rb_stats (int reset);
 #define DO_IF_RB_STATS(X) X
 #else
diff --git a/src/sprintf.c b/src/sprintf.c
index c1c5deee6b6499c67c40c347c54b8b0de23ff110..f1f5607cda58f01c65785ddc9ddaa5355efa3eae 100644
--- a/src/sprintf.c
+++ b/src/sprintf.c
@@ -2833,7 +2833,7 @@ void f___handle_sprintf_format(INT32 args)
 /*! @endmodule
  */
 
-void init_sprintf()
+void init_sprintf(void)
 {
   struct pike_string *attr;
   struct svalue s;
@@ -2881,6 +2881,6 @@ void init_sprintf()
 	    0);
 }
 
-void exit_sprintf()
+void exit_sprintf(void)
 {
 }
diff --git a/src/stralloc.h b/src/stralloc.h
index 666ebd7b3a95b04ed6390a9dac0a428969538cc7..076e39fb30f040dc44f8d7154eddd60780fa21e8 100644
--- a/src/stralloc.h
+++ b/src/stralloc.h
@@ -536,7 +536,7 @@ static INLINE int __attribute__((unused)) string_has_null( struct pike_string *x
 PMOD_EXPORT void f_sprintf(INT32 num_arg);
 void f___handle_sprintf_format(INT32 args);
 void low_f_sprintf(INT32 args, int compat_mode, struct string_builder *r);
-void init_sprintf();
-void exit_sprintf();
+void init_sprintf(void);
+void exit_sprintf(void);
 
 #endif /* STRALLOC_H */
diff --git a/src/threads.c b/src/threads.c
index b4ae9a0bcbeddf9380456fe784425de5cbb0c9de..8a82fa5c9e6c4ade5b8170f04174f8089c1968c0 100644
--- a/src/threads.c
+++ b/src/threads.c
@@ -62,7 +62,7 @@ static struct Pike_interpreter_struct static_pike_interpreter;
 PMOD_EXPORT struct Pike_interpreter_struct *Pike_interpreter_pointer =
   &static_pike_interpreter;
 
-PMOD_EXPORT struct Pike_interpreter_struct * pike_get_interpreter_pointer()
+PMOD_EXPORT struct Pike_interpreter_struct * pike_get_interpreter_pointer(void)
 {
     return Pike_interpreter_pointer;
 }
diff --git a/src/version.c b/src/version.c
index e63d2e712ae24c1c1055e4470b3b066e2471ba61..883e2c4ec7e07cb10baa6c08f1014f992d75e89d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -33,7 +33,7 @@ PMOD_EXPORT void f_version(INT32 args)
 		      DEFINETOSTR (PIKE_BUILD_VERSION));
 }
 
-void push_compact_version()
+void push_compact_version(void)
 {
   push_constant_string_code (str, {
       str = begin_wide_shared_string (3, 2);
diff --git a/src/version.h b/src/version.h
index a14ec9253393828c8e66382dd098615dc656a2d7..de92bf26685ac89d93cba19a51696d7d6ee00da2 100644
--- a/src/version.h
+++ b/src/version.h
@@ -13,5 +13,5 @@
 
 /* Prototypes begin here */
 PMOD_EXPORT void f_version(INT32 args);
-void push_compact_version();
+void push_compact_version(void);
 /* Prototypes end here */