diff --git a/src/core/testboxes.c b/src/core/testboxes.c
index dd5a3ed5e..94da52b6b 100644
--- a/src/core/testboxes.c
+++ b/src/core/testboxes.c
@@ -30,7 +30,7 @@
 #define NUM_RANDOM_RUNS 10000
 
 static void
-init_random_ness ()
+init_random_ness (void)
 {
   srand(time(NULL));
 }
@@ -99,7 +99,7 @@ new_monitor_edge (int x, int y, int width, int height, int side_type)
 }
 
 static void
-test_area ()
+test_area (void)
 {
   MetaRectangle temp;
   int i;
@@ -116,7 +116,7 @@ test_area ()
 }
 
 static void
-test_intersect ()
+test_intersect (void)
 {
   MetaRectangle a = {100, 200,  50,  40};
   MetaRectangle b = {  0,  50, 110, 152};
@@ -144,7 +144,7 @@ test_intersect ()
 }
 
 static void
-test_equal ()
+test_equal (void)
 {
   MetaRectangle a = {10, 12, 4, 18};
   MetaRectangle b = a;
@@ -163,7 +163,7 @@ test_equal ()
 }
 
 static void
-test_overlap_funcs ()
+test_overlap_funcs (void)
 {
   MetaRectangle temp1, temp2;
   int i;
@@ -186,7 +186,7 @@ test_overlap_funcs ()
 }
 
 static void
-test_basic_fitting ()
+test_basic_fitting (void)
 {
   MetaRectangle temp1, temp2, temp3;
   int i;
@@ -357,7 +357,7 @@ get_monitor_edges (int which_monitor_set, int which_strut_set)
 
 #if 0
 static void
-test_merge_regions ()
+test_merge_regions (void)
 {
   /* logarithmically distributed random number of struts (range?)
    * logarithmically distributed random size of struts (up to screen size???)
@@ -579,7 +579,7 @@ verify_lists_are_equal (GList *code, GList *answer)
 }
 
 static void
-test_regions_okay ()
+test_regions_okay (void)
 {
   GList* region;
   GList* tmp;
@@ -665,7 +665,7 @@ test_regions_okay ()
 }
 
 static void
-test_region_fitting ()
+test_region_fitting (void)
 {
   GList* region;
   MetaRectangle rect;
@@ -709,7 +709,7 @@ test_region_fitting ()
 }
 
 static void
-test_clamping_to_region ()
+test_clamping_to_region (void)
 {
   GList* region;
   MetaRectangle rect;
@@ -826,7 +826,7 @@ rect_overlaps_region (const GList         *spanning_rects,
 gboolean time_to_print = FALSE;
 
 static void
-test_clipping_to_region ()
+test_clipping_to_region (void)
 {
   GList* region;
   MetaRectangle rect, temp;
@@ -888,7 +888,7 @@ test_clipping_to_region ()
 }
 
 static void
-test_shoving_into_region ()
+test_shoving_into_region (void)
 {
   GList* region;
   MetaRectangle rect, temp;
@@ -1005,7 +1005,7 @@ verify_edge_lists_are_equal (GList *code, GList *answer)
 }
 
 static void
-test_find_onscreen_edges ()
+test_find_onscreen_edges (void)
 {
   GList* edges;
   GList* tmp;
@@ -1138,7 +1138,7 @@ test_find_onscreen_edges ()
 }
 
 static void
-test_find_nonintersected_monitor_edges ()
+test_find_nonintersected_monitor_edges (void)
 {
   GList* edges;
   GList* tmp;
@@ -1227,7 +1227,7 @@ test_find_nonintersected_monitor_edges ()
 }
 
 static void
-test_gravity_resize ()
+test_gravity_resize (void)
 {
   MetaRectangle oldrect, rect, temp;
 
@@ -1329,7 +1329,7 @@ test_gravity_resize ()
 
 #define EPSILON 0.000000001
 static void
-test_find_closest_point_to_line ()
+test_find_closest_point_to_line (void)
 {
   double x1, y1, x2, y2, px, py, rx, ry;
   double answer_x, answer_y;
@@ -1381,7 +1381,7 @@ test_find_closest_point_to_line ()
 }
 
 int
-main()
+main(void)
 {
   init_random_ness ();
   test_area ();