diff --git a/mopchk/mopchk.c b/mopchk/mopchk.c
index 7455c1e..065132d 100644
--- a/mopchk/mopchk.c
+++ b/mopchk/mopchk.c
@@ -65,7 +65,7 @@ char	*Program;
 
 extern char version[];
 
-void
+int
 main(argc, argv)
 	int     argc;
 	char  **argv;
@@ -158,7 +158,7 @@ main(argc, argv)
 			};
 		}
 	}
-
+	return 0;
 }
 
 void
diff --git a/mopd/mopd.c b/mopd/mopd.c
index 61493be..01f31d2 100644
--- a/mopd/mopd.c
+++ b/mopd/mopd.c
@@ -75,7 +75,7 @@ int	Not4Flag = 0;		/* Not MOP V4 messages.       */
 int	promisc = 1;		/* Need promisc mode    */
 char    *Program;
 
-void
+int
 main(argc, argv)
 	int     argc;
 	char  **argv;
@@ -187,6 +187,7 @@ main(argc, argv)
 		deviceInitOne(interface);
 
 	Loop();
+	return 0;
 }
 
 void
diff --git a/mopprobe/mopprobe.c b/mopprobe/mopprobe.c
index d5d9472..f5dcc0a 100644
--- a/mopprobe/mopprobe.c
+++ b/mopprobe/mopprobe.c
@@ -72,7 +72,7 @@ int     oflag = 0;		/* print only once             */
 int	promisc = 1;		/* Need promisc mode           */
 char	*Program;
 
-void
+int
 main(argc, argv)
 	int     argc;
 	char  **argv;
@@ -129,6 +129,7 @@ main(argc, argv)
 		deviceInitOne(interface);
 
 	Loop();
+	return 0;
 }
 
 void
diff --git a/moptrace/moptrace.c b/moptrace/moptrace.c
index 90a79cf..378e487 100644
--- a/moptrace/moptrace.c
+++ b/moptrace/moptrace.c
@@ -71,7 +71,7 @@ int	Not4Flag = 0;		/* Ignore MOP V4 messages      */
 int	promisc = 1;		/* Need promisc mode           */
 char	*Program;
 
-void
+int
 main(argc, argv)
 	int     argc;
 	char  **argv;
@@ -126,6 +126,7 @@ main(argc, argv)
 		deviceInitOne(interface);
 
 	Loop();
+	return 0;
 }
 
 void