diff --git eratspeed.c eratspeed.c
index 3bad129..08fe934 100644
--- eratspeed.c
+++ eratspeed.c
@@ -1,6 +1,7 @@
 #define B32 1001
 #define B (B32 * 32)
 
+#include <stdio.h>
 #include "timing.h"
 #include "uint32.h"
 
@@ -400,7 +401,7 @@ void countit()
 timing t;
 timing told;
 
-main()
+int main()
 {
   int L = 1;
 
@@ -432,5 +433,5 @@ main()
   printf("Overall seconds: approximately %f.\n",0.000000001 * timing_basic_diff(&finishb,&startb));
   printf("Tick counts may be underestimates on systems without hardware tick support.\n");
 
-  exit(0);
+  return 0;
 }
diff --git primegaps.c primegaps.c
index c040611..190d6b1 100644
--- primegaps.c
+++ primegaps.c
@@ -1,9 +1,10 @@
+#include <stdio.h>
 #include <math.h>
 #include "primegen.h"
 
 primegen pg;
 
-void main()
+int main()
 {
   uint64 p;
   uint64 lastp;
diff --git primes.c primes.c
index b8b0461..a9cd8e5 100644
--- primes.c
+++ primes.c
@@ -36,7 +36,7 @@ primegen pg;
 uint32 digits[40];
 int len;
 
-void main(argc,argv)
+int main(argc,argv)
 int argc;
 char **argv;
 {
@@ -88,5 +88,5 @@ char **argv;
     putchar('\n');
   }
 
-  exit(0);
+  return 0;
 }
diff --git primespeed.c primespeed.c
index 3d16c04..294f120 100644
--- primespeed.c
+++ primespeed.c
@@ -1,3 +1,4 @@
+#include <stdio.h>
 #include "timing.h"
 #include "primegen.h"
 #include "primegen_impl.h"
@@ -89,7 +90,7 @@ timing_basic startb;
 timing finish;
 timing_basic finishb;
 
-void main(argc,argv)
+int main(argc,argv)
 int argc;
 char **argv;
 {
@@ -118,5 +119,5 @@ char **argv;
   printf("Overall seconds: approximately %f.\n",0.000000001 * timing_basic_diff(&finishb,&startb));
   printf("Tick counts may be underestimates on systems without hardware tick support.\n");
 
-  exit(0);
+  return 0;
 }