diff --git a/configure.ac b/configure.ac
index 6477ec1..9766467 100644
--- a/configure.ac
+++ b/configure.ac
@@ -233,6 +233,23 @@ then
 	)
 fi
 
+CFLAGS="$cstd -Wmissing-prototypes -Werror"
+AC_MSG_CHECKING([whether CC supports -Wmissing-prototypes])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([])],
+    [AC_MSG_RESULT([yes])]
+    [cstd="$cstd -Wmissing-prototypes"],
+    [AC_MSG_RESULT([no])]
+)
+
+# XXX AC_LANG_PROGRAM produces unsuitable prototype so this check must be last one
+CFLAGS="$cstd -Wstrict-prototypes -Werror"
+AC_MSG_CHECKING([whether CC supports -Wstrict-prototypes])
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[int main(void) { return 0; }]])],
+    [AC_MSG_RESULT([yes])]
+    [cstd="$cstd -Wstrict-prototypes"],
+    [AC_MSG_RESULT([no])]
+)
+
 CFLAGS="$oldcflags"
 
 AC_ARG_ENABLE([binfilterlen],
diff --git a/ed25519/ed25519.h b/ed25519/ed25519.h
index d0c4491..f59760f 100644
--- a/ed25519/ed25519.h
+++ b/ed25519/ed25519.h
@@ -36,7 +36,7 @@ static const ge_cached ge_eightpoint = {
     11267669, -24569594, 14624995
   }
 };
-inline static void ge_initeightpoint() {}
+inline static void ge_initeightpoint(void) {}
 #endif
 
 
@@ -105,7 +105,7 @@ static const ge25519_pniels ge_eightpoint = {
 	// t2d
 	{{ 1700965895112270, 372560131616985, 329575203620664, 756160485635107, 981466775886086 }},
 };
-inline static void ge_initeightpoint() {}
+inline static void ge_initeightpoint(void) {}
 #endif
 
 
@@ -129,7 +129,7 @@ static const ge25519_pniels ge_eightpoint = {
 	// t2d
 	{{ 9713713562319586894U, 4328467261753610859U, 8262494979546083277U, 4020087914029409631U }},
 };
-inline static void ge_initeightpoint() {}
+inline static void ge_initeightpoint(void) {}
 #endif
 
 
@@ -232,7 +232,7 @@ static u8 fe_t2d[32] = {
 };
 
 // initialize from packed representation
-static void ge_initeightpoint()
+static void ge_initeightpoint(void)
 {
 	memset(&ge_eightpoint,0,sizeof(ge_eightpoint));
 	curve25519_expand(ge_eightpoint.ysubx,fe_ysubx);
diff --git a/filters.h b/filters.h
index ffd4c75..71f0118 100644
--- a/filters.h
+++ b/filters.h
@@ -92,4 +92,5 @@ extern struct pfiltervec filters;
 extern int flattened;
 
 extern void filters_init(void);
+extern void filters_add(const char *filter);
 extern size_t filters_count(void);
diff --git a/main.c b/main.c
index 8f3cdd7..355f935 100644
--- a/main.c
+++ b/main.c
@@ -114,14 +114,14 @@ static void printhelp(FILE *out,const char *progname)
 	fflush(out);
 }
 
-static void e_additional()
+static void e_additional(void)
 {
 	fprintf(stderr,"additional argument required\n");
 	exit(1);
 }
 
 #ifndef STATISTICS
-static void e_nostatistics()
+static void e_nostatistics(void)
 {
 	fprintf(stderr,"statistics support not compiled in\n");
 	exit(1);
diff --git a/yaml.c b/yaml.c
index 1f9e983..ebe03ab 100644
--- a/yaml.c
+++ b/yaml.c
@@ -49,12 +49,12 @@ static const char keys_field_time[]      = "time: ";
 
 static pthread_mutex_t tminfo_mutex;
 
-void yamlout_init()
+void yamlout_init(void)
 {
 	pthread_mutex_init(&tminfo_mutex,0);
 }
 
-void yamlout_clean()
+void yamlout_clean(void)
 {
 	pthread_mutex_destroy(&tminfo_mutex);
 }
diff --git a/yaml.h b/yaml.h
index 0dc75d5..ca356c5 100644
--- a/yaml.h
+++ b/yaml.h
@@ -1,4 +1,4 @@
-extern void yamlout_init();
-extern void yamlout_clean();
+extern void yamlout_init(void);
+extern void yamlout_clean(void);
 extern void yamlout_writekeys(const char *hostname,const u8 *formated_public,const u8 *formated_secret);
 extern int yamlin_parseandcreate(FILE *fin,char *sname,const char *hostname);